I see legitimate well founded arguments on both sides of this...
Really? I'd like to see a well founded argument for Motti's effect sticking around after he's gone. Because so far I haven't seen one. Again, it's well established that upgrade effects only apply as long as the upgrade in question is in play.
There is not a single example of an upgrade effect surviving the card being removed. The gamestate the upgrade creates may continue, like exhausting or even discarding something, but there is no ongoing effect that sticks around after the card itself is removed from play.
They would still be alive even without Motti. Its all part of the game.
The whole point of Motti is to improve the tankyness of his fleet. That's a attribute that may not factor into a game at all, either because you're hopelessly out gunned, and the extra hull doesn't really help at all, or you may never need it.
Trying to argue that his ability should stick around just because it may not be used otherwise, is quite possibly the most illogical argument I've heard.
Dodonna's ability only comes into play if you get a crit though. Screed's ability only comes into effect if you want to spend a die to trigger it. Likewise Motti's ability only comes into effect when a ship has been dealt enough damage cards to kill it, without his buff.