Also, there is a timing aspect here. The expansion drafts are usually in Nov-Dec, right after the season ends and prior to the superdraft. I get that there is a deadline where he has to enter the superdraft, but it is possible we could protect Dax, then trade him, then sign Sean Davis a week/month later, before he gets drafted. I really doubt we'd have to make an 'either-or' decision unless we really screwed up the timing on our roster lists. Also note, homegrowns are protected from an expansion draft, so, it's not that they would select Sean Davis, but rather that we would protect or not protect Dax.
That said...Dax makes a lot of money and is an integral part of our team. If ORL comes in and offer top $$ for him, you have to do that, but, I'd rather keep him a year or two and let the Sean Davis/Etc. people grow, and then trade Dax (even if it is for less than we'd get this off-season) next year so that we're not exposed with having to start rookies (or, Eric Alexander) in central midfield.
Trades with Orlando will be tricky, however, as they don't currently have a team. It's not like you can go to LA and say "give me De La Garza straight up" or something. You're really looking at trading for draft picks, allocation cash or something else (unless you want Yordany Alvarez back in a trade).
Let's assume TH14 retires. They could move Cahill up top, put us into a 4-4-2, and find 1 solid box to box guy to play alongside Dax. Then maybe we'd be a team with a better shape, and fewer issues. In that case, sending Dax to Orlando gives us 2 holes to fill, not 1.