I think he'll fight it. I don't think he'll plead. He's shown he's stubborn (or stupid? or brave?) enough to not play along, and enjoys holding up a mirror to show how sleazy and evil the rest of the "elites" are. He'll keep fighting especially since it's giving Trump the only two things he loves: 1) publicity and 2) money. It's boosted his campaign donations.
I think eventually "they" i.e. the parts of the establishment that want him out of the picture will either escalate the case against him by adding new charges, or targeting his kids.
Or they might assassinate him. Or he could also just die (he'll be 77 in a couple months).
He might not care about the personal consequences at this point (at 77, his legacy is more wrapped up in this) and fight to the end. Even if convicted, he could run for president (Eugene Debs ran from prison in 1920 and received the 3rd most votes in that election; around 3.5% of the total popular vote).
I think the powers that be will push the DA to quietly drop charges after a few months, when they see that this has been more of a benefit than a detriment to Trump. The media will generally blackout the decision