Trump simply cannot answer questions under oath without disastrous consequences. He suffers from dementia, so he can't answer questions on topics much more complicated than what club to use off the tee on the 5th hole at Mar-a-Lago without perjuring himself right and left. Yet he can't admit that he suffers from a dementia so advanced that he can't answer questions about presidential and business decisions his handlers have pretended were his. That admission would require that the people who are supposed to make the 25th work, proceed to make the 25th work.
His obvious play is to simply refuse to answer questions under oath. I should say, his handlers' obvious play is to make that decision on his behalf. Whatever the consequences of ignoring subpoenas and court orders might be, they can't possibly be worse than letting a demented person answer Mueller's questions under oath. If it comes to it, even a SCOTUS order to testify should be met with a statement to the effect that "Mr. Justice Roberts has made his decision, now let him enforce it."
Unfortunately for his handlers, the current state of Trump’s dementia has left him a stable genius, easily the smartest person in any room. Convincing him that he can’t easily outmaneuver Mueller's questioning is going to be a tough sell for his handlers. They may be forced to resort to the ploy of making it a status thing. No way can he wimp out and be the first president to agree to testify in a criminal investigation while still in office
The only approach I see working aside from simple refusal to testify, would be for Trump to agree to testify but then simply deny remembering anything when he is questioned. This isn't nearly as simple as it might seem though, because for it to work, he has to stick rigidly to denying that he can remember every single individual thing he's asked about. Admitting that he remembers even something that he imagines is harmless, opens him up to follow-up questioning along that line, and somewhere down the line he gets into matters that will inadvertently lead to perjury no matter how he tries to answer. Judging when to to stop, when he would have to start claiming that he can't remember, is exactly the sort of judgment that he can no longer make competently, not even up to the level of a kindergartener. This strategy only works if he is able to stick with not remembering things as a rigid and categorical approach under questioning.
The handlers would also have a tough time selling him on this strategy. Why can’t he just wing it? A stable genius like he is, of course he can stonewall with the “I don’t recall" line where that’s smart, but then answer cleverly where he sees an opportunity to trip up Mueller. Piece of cake for the Art of the Deal guy. Based on the evidence of a taped deposition that I have seen, though, his handlers did get him to take this approach in the past in one of his lawsuits dealing with one of his business frauds. Maybe they can get him to perseverate.
This strategy is different from admitting dementia in that there is no categorical claim to not being able to remember things as the result of any sort of disability. He just denies remembering the particulars of every single individual thing he's asked. Intelligent observers could certainly detect a pattern, by way of inductive reasoning, suggesting that this person who can't remember anything he's asked about may be demented. But, hey, most of us have so far managed to ignore all the evidence pointing in that direction. There are all sorts of reasons the people who are supposed to make the 25th work have decided not to make the 25th work, despite that mound of evidence that this president is unfit for the office, is cognitively incompetent and dysfunctional in that office. That Trump testifies under oath and doesn't remember anything at all, is not going to remove any of those reasons to not make the 25th work. As long as he doesn't say he's demented, he can go on giving every evidence in word and deed that he is demented, and the system will let it slide.