It may well be a crazy game of chicken right up until they make their pick. If they trade Fields at this point, it gives away the game that they're taking QB at 1 and almost certainly CW. They lose any trade leverage they have, but maybe they don't care if Caleb is their guy and they're set on making the pick.
At this point, their best bet may be to keep Fields for now, see if somebody blinks and makes them the proverbial Godfather offer on draft night and take the best QB available wherever they land in terms of the trade.
That also gives them the ability to get max value on the clock if one of the teams that misses on the top guys on their board (that could be 3 guys, 6 guys, or any number in between) and decide to call the Bears for Fields. Say maybe the Giants go WR at 6OA, expecting Penix or Nix to be there at their 2nd rounder. If those guys end up going in the first -- very possible -- they either have to call CHI or settle for a Rattler or Pratt, and maybe having to spring earlier than they're worth. At that point, Bears are in the catbird seat.
This draft night is going to be must-see.