(CNN) The Russians are investigating whether one of their airstrikes against ISIS targets south of the Syrian city of Raqqa last month may have killed the group's leader, Abu Bakr al-Baghdadi.

IF Baghdadi were killed, the death of the self-declared "Caliph" would be a huge symbolic loss, and a blow to the concept of an "Islamic State" of which he was the figurehead.

But in terms of ISIS' future as a terrorist group and a source of inspiration, whether Baghdadi is alive or dead might not matter that much. And that cuts both ways. It speaks to both ISIS' grim -- and probably irretrievable -- situation on the battlefields of Syria and Iraq, but also the resilience of its message in jihadi circles worldwide. Just as al Qaeda survived the death of Osama bin Laden and a raft of other prominent figures, so ISIS is more than Baghdadi.

Not dead yet?

Of course, rumors of Baghdadi's demise have been exaggerated in the past -- notably early in 2015, when attention focused on possible successors

He subsequently provided "proof of life" in an audio message about the battle for Mosul late last year.

It is true that Russian airpower has been very active in the past two weeks in desert areas between Raqqa and Palmyra. At the end of May, cruise missiles were launched from the Mediterranean to take out an ISIS convoy, according to the Russian Defense Ministry, which has also reported strikes against bunkers and caves used by ISIS in this region.

Even so, were it the case that Baghdadi had died, it is puzzling that no rumors, let alone any official announcement, have surfaced in the 18 days since the Russians say the strike occurred. All the more so if the target was such a large meeting of ISIS' leadership as the Russian Defense Ministry states.

Setting such doubts aside, any ISIS leader -- Baghdadi or otherwise -- would see a battlefield of retreat and disarray.

Collapsing caliphate

ISIS' deteriorating position in both Syria and Iraq has accelerated in recent months as it has lost territory and suffered huge casualties from intensified air and ground campaigns.

Most of its remaining fighters are either on the run, seeking new refuges in which to regroup, or holed up in grinding urban combat. Its leadership has been scattered, its once pervasive administrative machine obliterated, its ability to attract reinforcements from abroad stifled.

In part this is because of a more aggressive approach by US-led coalition forces. As US Secretary of Defense James Mattis put it last month: "We have already shifted from attrition tactics, where we shove them from one position to another in Iraq and Syria, to annihilation tactics where we surround them."

In Iraq, "dead-ender" fighters, maybe now in the low hundreds, are clinging on to a patch of western Mosul around the mosque where Baghdadi declared himself the caliph almost exactly three years ago. Further west, Iraqi Shia militias have moved into the empty spaces of Anbar province, which has often been suggested as a hiding place for Baghdadi.

In Syria, ISIS has faced multiple enemies as it has lost its grip on areas of Aleppo province and the Raqqa countryside. With every passing week its fighters have been pushed further away from the Turkish border, once a critical source of supplies and fresh fighters. In the last two weeks alone, it has lost considerable territory to both the Syrian army and the US-backed rebel Syrian Democratic Forces. The latter have made surprisingly rapid progress in taking neighborhoods of Raqqa itself.

One example: it appears at least some ISIS leaders recently tried to regroup east of Raqqa, around the town of Mayadin. One of them was a senior religious figure, Turki al-Binali . Sources told CNN recently that he'd been killed in a coalition airstrike, and other media reported that Rayan Meshaal, the founder of the ISIS-affiliated Amaq news agency, was also killed in the area. The US-led coalition spoke of airstrikes at the end of May aimed at ISIS propaganda production facilities.

None of this means that ISIS can be consigned to the dustbin of history -- but its control of real estate is evaporating.

On message

The group's leadership has long acknowledged it might come to this, but changed the narrative to insist that territory is less important than the "will to fight."

In May 2016, ISIS spokesman and senior official Abu Mohammed al-Adnani declared in an audio message: "Would we be defeated and you be victorious if you were to take Mosul or Sirte or Raqqa or even take all the cities and we were to return to our initial condition? Certainly not! True defeat is the loss of willpower and desire to fight."

The message was repeated last November in a recording purportedly from Baghdadi himself. At that stage, he was offering the prospect of glory in martyrdom rather than a shining city on a hill. "Holding your ground in honor is a thousand times better than retreating in disgrace," he said.

To a group fixated on the "end of days" and apocalyptic battles against "crusader" armies, this is not much more than a bump in the road. As one former jihadist puts it, "It's not what you or I believe that matters; it's what they believe."

ISIS lives on

Even if Baghdadi were dead, ISIS would not be. It has:

An ideology that certainly still has its adherents and can inspire at least some young Muslims in the West to acts of terror

Networks whose cells are still capable of monstrous terror attacks (in Baghdad and Kirkuk, for example); and that are showing signs of regenerating in provinces like Diyala in Iraq.

A label that is still embraced by jihadist groups as far afield as Egypt, Libya, Afghanistan and the Philippines. ISIS has claimed terror attacks in Kabul and Tehran in recent days, and three weeks after first entering the Philippines town of Marawi, fighters pledging allegiance to the group have still not been evicted by the Philippines army.

Certainly, ISIS' raison d'etre -- and what distinguished it from groups like al Qaeda -- was to create and administer a caliphate, and to demand the obedience of all Muslims to the "righteous" caliph, one Abu Bakr al-Baghdadi. The phrase "remaining and expanding" was its dogma.

It was Binali himself who said in 2013: "Doubtless, the caliphate requires some measure of power, might, and political capability, and this is present in the Islamic State."

It's scarcely present any more, but the message still echoes for those who wish to hear it, that the righteous (as Adnani put it) "are always and forever victorious, since the battle of Noah and until Allah inherits the earth and those upon it."

In other words, it doesn't really matter how many Baghdadis are killed.