Lukaku's performance in intermilan was not so bad as you said. Even though lukaku has failed to bring intermilan to win UCL but his performance was quite well last season. Intermilan was winning a trophy + it has gone to the final of UCL which was a great achievement by intermilan. The only problem if lukaku never had interest to join in ac milan. Acmilan was making the wrong decision to tageting him as a new striker for the club.
I think that ac milan shall not try to take lukaku. Ac milan must have found another player that can become a new striker for ac milan upcoming season. Lukaku will never ever fit for the club. He is only wanna playing for intermilan.
Even he rejects to play for chelsea and he was only going for intermilan. Chelsea even ac milan must retain themselves in using this guy as striker.
I doubt with Milan has enough money for signing Lukaku due should fight with Saudi Pro League team give bid for buying Lukaku from Chelsea, its seems dilemma for Lukaku position right now, he has denied for playing with Saudi Pro League teams but his previous team Chelsea want to sell him there. Right now the future from Lukaku depend on Inter Milan want to pay higher fees transfer for Chelsea or Lukaku will return back as loan option from Inter Milan. Inter should keep him stay for one year later after leaving by Edin Dzeko, Inter's attacking line only left Lutaro Martinez right now.
For Lukaku performance in this season not really bad, he has success bring Inter lead to final stage in Champion League but he got injured and absent on many game for Inter Milan.
It seems in this season Saudi teams are making trouble for the European teams and they are making players ask for higher amounts of money because they can get better offers from these Arabian teams, Lukaku can definitely be a good player for Milan but considering their financial situation I don't think if Milan can pay enough to Lukaku.