Don't expect Foster to step right in and start. Bucs better re-sign Ruud.
I expect him to be used frequently early on in the season, and eventually starting somewhere around midseason or so. Might not be MLB, but I think we have some solid backups who aren't likely to be any worse than Ruud.
I would consider bringing him back, but it depends on the price. If other teams overvalue him(and they likely will as his stats look great), I'd let him walk. We'll see what the market for him is.