How a team handles stomps and revives is basically the main difference between a good team and a great team. As an engineer your role is not to stomp but to cleave. Sure if your guardian gives you stability and you happen to be close it's fine to go for a stomp once in a while but usually you should be dropping bombs and grenades all over the downed guy. It's not uncommon to see teams with 3+ members downed after your team's cleave takes them all out.

If they are eating the cleave but actually getting somewhere feel free to use either shield skill to stop them. Usually they will have stability so it's easier to just cleave and save these skills but if you see an opportunity use it.

When a friendly goes down on your team you should throw an elixer R anytime it seems the revive won't be very easy. Same goes with dropping big ol' bomb near them. It prevents stomps and scares opposing players away. You generally want to try to revive if the opposing team doesn't have that much cleave in the fight you're at. If they do then usually stand back and counter pressure with damage and let the elixer R plus a more tanky member or 2 handle it. Prevent them from stomping with shield skills and big ol' bomb.

Sometimes the best option is to do nothing when an opposing member goes down. What I am referring to here is the concept of bleeding an opposing player out. This is done when the last enemy or two get's downed in a fight and reinforcements are nowhere insight. Usually if they die off point you can throw some condi's on them and just have 1 member keep an eye on them for a while. If they are dumb enough to try to self rez you can keep them locked out for large chunks of the game. If they die on point and you need them off point to cap it then use big ol' bomb to throw them clear and continue the timeout while capping. Just don't try this with rangers and get the stomp/finish if any opposing player enters your vision.