I understand that there is work supporting the idea that cryonics/regeneration/etc. will eventually be successful. However, I don't feel the need to respond to this work very directly, because this work, after all, is very indirect, in the sense that it is only making plausibility arguments.

In this case, indirect evidence is the only kind of evidence you can hope to obtain, so your current conclusion has to be formed based on indirect evidence. And this applies to any conclusion. If you believe that cryonics won't work, this is also based only on indirect evidence. It has to be.

Now, in most cases, the prior of a given idea not working is high enough, so we have a "by default" argument, believing something is impossible until proven possible. But this is a matter of framing: is it possible to implement a manned expedition to Mars, say? Is it possible to travel faster than light? The difference is always in intuitive estimation of detail that goes into the question, and what exactly is being asked matters. The "impossible by default" heuristic is a good tool, but has apparent points of failure, and you have to be aware of these where obtaining explicit evidence is not expected.