Coming back from the dead is rare - even among superheroes - Blackest Night would be far less populous and effective if it weren't - and entirely based on luck (or, rather, writer's whim), not cleverness, rarely even strength of will. Someone who was a Titan would know this better than most. The number of truly dead Titans is approximately twice the number who have died and come back. All of them (including Tim) have dead loved ones.
Yet, Tim thinks Bruce has got to be one of those oh-so-rare lucky ones who manages to crawl back, even before he gets evidence. That's not thinking rationally, that's getting stuck thoroughly in denial.
And I doubt Bruce is going to be happy about Tim abandoning the mission for this.