That's the concern about Lukaku, it could be that Lukaku's career might become very dim due to the lack of interest from other clubs. Because yes, if Lukaku is not recruited by another club and then, next season Lukaku will be at Chelsea but yes, because it seems like Lukaku doesn't have a good place in the first team then it seems like next season Lukaku will be more on the bench. If this is true, then of course Lukaku's career will fade but yes, because the transfer window is still long, it is possible that at the end of the transfer window there are other teams willing to recruit Lukaku.
Actually Inter still want Lukaku to be on the team it's just that at this time they don't have enough funds to contract him therefore Inter offers other options to Chelsea like extend the loan for 1 season, with a permanent contract option in the following season it's just that Chelsea haven't responded, maybe they are waiting for an offer from another club. reportedly Milan was also interested but there was no follow up.
Didn't Inter Milan have the money to buy Lukaku? I think Inter Milan can purchase Lukaku, but they are just thinking something else first. Although Lukaku is really good, I don't think Inter Milan will regret signing him since when he comes to Inter Milan, everyone seems to like what they see of his performance. I believe they want to extend the loan because they want to continue using Lukaku as they have this season and just don't want him.
Lukaku didn't perform well for Chelsea, and even if he returned, I think his output there wouldn't be any better than Inter Milan's. Therefore, I don't see what Chelsea would want him to accomplish for them.