I think he has a fair chance against Tavares, but seems like most people believe Tavares knocking him out is all but guaranteed.

I dunno, any particular result doesn't seem so obvious to me.
Brad doesn't have that much power, but Chris isn't all that durable these days. Regardless, while I think Tavares
can finish Chris, I don't think he has to. Tavares has better cardio and really good TDD. Since Romero took him down more or less at will and exposed him on the mat, Tavares focused a lot more heavily on his TDD and it's visibly paid off. Following that fight he has faced ten opponents who have tried to wrestle him in some fashion... with a combined 66 takedown attempts made against him in that time span. Of those attempts he has defended all but eight. His last few bouts have consisted of him relentlessly stuffing Omari Akhmedov, Dricus du Plessis, and Antonio Carlos Jr. (all three of which have 40-50% takedown accuracy across their career, mind you, which is solid or even above-average for a wrestler). I really do recommend watching these fights. The Dricus bout was more of a sloppy brawl, but the Omari bout and especially the Antonio Carlos Jr. one was a master class of defensive wrestling. It's MMAth, but Omari actually scored twice as many takedowns against Weidman as he did against Tavares, though to be fair Chris ultimately ended up out-grappling Akhmedov in the third round pretty decisively despite being fatigued.
When he
does get taken down, Brad is good at minding his P's and Q's and staying safe, keeping himself out of bad positions, and scrambling as rapidly as possible back to his feet. He has the 15th lowest bottom time percentage of all active Middleweights. He has never been submitted across his entire career either.
If this was the Chris of ten years ago, I'd say he makes a mockery of Brad's TDD and probably gets him down some way, somehow. That or at the very least he is able to use the threat of the takedown to outstrike him. But this version of Weidman we've seen recently... now coming off a terrible injury and a long lay-off... I dunno. People are right to be worried, especially against this particular opponent. Anything can happen in MMA, though. It'd be nice to see Chris turn back the clock, I just don't have much faith in him to do so.
Taveras is a guy that looks like he SHOULD have power but only has 2 KOs/TKOs in 20 UFC fights.
Yeah he is definitely not a power-puncher, lol. He's a guy who relies on volume, though to be honest he doesn't actually have crazy stats in the department either. That being said, I wouldn't be remotely surprised to see him get an attrition-based TKO against Chris late into Round 2 or in Round 3 if/when Weidman exhausts himself chasing takedowns and is there to get hit, allowing Brad to sit down on his punches and even string together combinations.