Nonsense. If we sold him at any point, we'd have brought in another player and played a different way.
The "Without Lukaku we'd get relegated" argument has no merit whatsoever.
We'd have gone down or at least got very close to going down without his goals, of that there is no doubt, to me anyway.
If we had sold him in the summer, I don't believe Martinez would have been able to replace with anyone of a similar level and we'd have ended up with a gamble, Niasse for example.