I don't think that Ellsbury "declining fast" is the risk you're making it out to be -- or the real reason you're concerned about retaining him.
Everyone wants the new toy. It's natural. but a team that has a player with an elite skillset in a highly applicable area generally doesn't throw that player away just because of the new toy. This plays into years-old issues between Ellsbury and the fanbase, and possibly Ellsbury and the team as well. There's been a rather guarded take on Ellsbury from the moment he ran into Beltre and smashed his ribs in 09, that's just a fact. The lion's share of the eagerness to move on, therefore, lies in the hope that we can have a centerfielder next year who is not Jacoby Ellsbury. One without some of the bad memories Ellsbury's picked up while he's bee
I'm sure the pick helps, but we don't even know what that pick will turn into. Draft picks are a crapshoot making that argument a minor factor at best. The money helps, but it's mostly an excuse to hide behind -- that money comes out of the FO's profit margins, if they want to spend it, it's there to be spent. I'd call that a nonfactor for the most part, except for perhaps how it plays into our pet theories about the guys we think the team should sign.
No, get down to meat of it, the real issue is that years-old antipathy for Ellsbury -- not really a hatred even, more of an unexpected ambivalence as near as I can determine. Certainly we should be more excited to have a player of that skill level than it turns out we are. The lion's share of the eagerness to move on, therefore, lies in the hope that we can have a centerfielder next year who is not Jacoby Ellsbury. One without some of the bad memories Ellsbury's picked up while he's been here. Draw your own reasonings on why, all of them are at least partly applicable, and none of them fully explain the issues that happen on a visceral level between a fanbase and a player.
The mere fact that we don't know whether or not JBJ has the same warts is the real core reason people are so anxious to move on here, whether they'll admit it or are even aware of it or not. And it's not a very good argument.