There is an unlikely scenario
Remember when Martinez said he sees this window as a short term fix opportunity?
We do have money from the summer and now from Jellavic's sale, yet he is not spending anything, it the Jones story is true, it means he is looking for a cheap backup, not a long term 1st choice striker
That takes us to Lukaku, regardless of what Martines is saying, he will LOVE to sign him permanently, and regardless of what both Lukaku and Mourinho say, the relationship between the both is damaged and knowing Mourinho who deosn't tolerate criticism from a 30+ years old club legend let alone a 20 years old kid, i can't see Lukaku going back to Chelsea under Mourinho and becoming regular and i doubt Mourinho will leave Chelsea anytime soon.
Lukaku is obviously enjoying his time here (check this out
https://twitter.com/RomeluLukaku9/status/419591854469156864 ) he is still 20 and a smart boy, he knows very well that being a regular for Everton is better than a backup for Chelsea or Barcelona or Madrid (at this stage of his career) so if he has no future at Chelsea under Mourinho he will gladly move here permanently
As we are seeing with De Bruyne, Mourinho has no problem in selling one of the youngsters that was brought to the club by someone else, De Bruyne like Lukaku is highly rated but is being sold, Lukaku and De Bruyne are Belgians and same age so i think if they are not closed friends at least they speak with each others, De Bruyne was somehow forced out of the club by Mourinho.
So that leaves us with one small problem, around 15-20M of real money, is Martines saving all the money to spend it on Lukaku in the summer? Or if Lukaku goes back to Chelsea on another 15-20M striker?