I saw a report today (not sure how true) that the Woodruff is the pitcher teams think may be dealt and that the Brewers intend on keeping Burnes at this time and negotiating an extension with him. It's interesting, because, financial considerations aside, Burnes, at 28, is the one you'd ideally sign-long term, while Woodruff, who will turn 30 by spring training, is the one you'd prefer to trade. So, IF TRUE, maybe they anticipate something closer to what you're saying, i.e. a DeGrom-type extension at 5 years, $130 million+, which would allow him to reenter free agency and sign a second big-money deal at 33. That is not out of the Brewers' range....
Also, I would point to the extension Jose Ramirez signed with Cleveland just before the season. Different positions and ages, yes, but Ramirez was looking at a huge deal in free agency and instead re-upped one year-out with the only club he has ever known for 5 years, $124 million. It is entirely possible that Burnes could decide to do something similar.