The problem with this thread (and threads like it) is that people keep conflating three different scenarios:
1) The player is already signed long term AND his current team has no need to trade him. In this scenario the player’s value is at its highest; if this were the case then of course neither Foote nor Johnson would be sufficient on their own to return Trouba.
2) The player is already signed long term BUT his current team has to trade him. This is usually because a team has cap issues and needs to trade a player already under contract to create space; it would also include the mythical “sign and trade” situation that fans of teams with impending UFAs always insist will happen but which never actually occur in real life. The player’s market value is lowered in most cases because his current team no longer has the option of keeping him if they don’t like the best offer (you can think of that option as a reserve price in an eBay auction: with it you’re assured of at least getting the minimum price you’d be happy with, but without it you’re stuck taking the highest bid whether or not you like it.) In this case Trouba’s value would depend on the number of bidders and how high they would be willing to go; from Tampa’s perspective we could afford to give up Foote in this scenario because we’d be assured of getting Trouba on a long term deal.
3) The player is being traded without an extension in advance. In this scenario the player’s value is significantly lower even with a verbal agreement on an extension (a “trade and sign”, which unlike the mythical “sign and trade” actually happens in the real world) because the buying team has no guarantee beyond the years currently on the player’s contract. In this case Trouba would certainly not return Foote; Johnson might be a possibility IF the Lightning were either willing to gamble that they can convince Trouba to resign or wanted to use Trouba for a Cup run or two and then use the freed up cap space for some other purpose.
Since “sign and trades” don’t happen in the real world and Trouba won’t be extended unless the Jets can afford to keep him, scenario 2 doesn’t apply here. So it all comes down to whether or not you think a longterm deal between Trouba and the Jets is realistic. If you think it is then a trade isn’t going to happen in the first place, but if a trade does happen it will be under scenario 3 and Trouba’s market value will be based on his remaining term, NOT what his value would be with a longterm deal.