The thing is, Regardless of technicality and legal accuracy (and i doubt competent lawyers already sacked by bartomeu for saying the same, woukd go this public if they werent damb well confident they were right) Messi now has all the moral high ground here, 100% of it.
He in good will acted on a contract. When bartomeu refused to accept that, he reportedly had his canp offer a negotiated amicable way out. Whether thise clains were briefed, leaked, speculated or fabricated, does not matter in the slightest now, they are out there and will stick, that he tried to do right by the club in a grown up way. And bartomeu refused and decided to stick purely to contract.
So now, as contract allows, he can in no way be seen as having screwed barca over or cost them a transfer fee, just that he took the privilege legally afforded to him, after having explored other options first. Nobody can hold that against him, he can leave with or without a goodbye without a stain on his legacy.