I think Advent already have phase jump inhibitors, mass disorientation and repulse to keep enemy ships from fleeing.

Is there some sort of middle ground then? It seems that the way it works now is underpowered, as the enemy can flee rather easily, and then you are out one titan.

I think it should get a 500% damage return...
kinda like the Rapture Battlecruiser.

and maybe a +250 Shield Restore per second

Disabling phase engines might work - your opponent could still run around the gravwell, though Repulsion could give them enough trouble to make the ability OP.

Seems like a simple fix would be to allow manual activation before the titan reaches 0HP (it would still die at the end).  That way, you opponent can't turn around and finish it off with bombers after they're safely away.

However, I'm still inclined to favor a weaker version that either requires the titan to be below 25% hull or gets stronger the less hull you have (but doesn't kill the titan or make it invulnerable).