not that he'd die, but that he'd... that he'd be out of the story for long enough that it'd throw off all the narrative weights and he'd get crowded out as a main character and it would ruin my polyamory hopes
"I might have known!" is very Othar, and also since Gil is going in to retrieve Tarvek (presumably) I didn't think he'd react to him like that in this particular situation.
And we don't exactly know how much Gil knows about Tarvek getting poisoned, since Klaus shut him down somewhere during that message, but presumably that's going to be relevant.