Surly that depends on how he performs, the facts are he’s had some serious injuries, and he hasn’t had a decent season for 3-4 years, either way there are risks but a year loan would seem a lesser risk than a 3-4 year deal on a player that may breakdown and not live up to his billing.
Lukaku signed after a good loan spell why wouldn’t he, if he has a good loan season because of the manager who he respects play’s to his strengths and the team is improving, I would expect him to want to stay, same as Gomes sometimes enjoying your football and feeling wanted out ways going to a bigger team and sitting on the bench.