Well..i had it for a few hours and what not, and spent a little time getting it to be friendly. But I'd say I got killed maybe 4-5 times in Thor, and then when i respawned, it was gone ._.;
Like Vanadis said, it most likely lost too much intimacy and ran away, you lose intimacy when you die, when you egg the pet, or feed it at the wrong time.
he only had it for a few hours, so I doubt Dosu got that much opportunity to feed it that many times to gain some intimacy point to fight off like 5 deaths x_X; Not to mention, deviruchi is not a low level pet like a drop either.
Best way to get it replaced: Hunt Jokers or use celebration wings (to farm Pet Taming Gift sets) and hope you get lucky on Contracts in Shadow, then go to geffen 3, geffen 4, geffenia, or geffen guild dungeon and hope you get lucky with taming another one