Sorry but, even though it causes me immense pain, I have to agree with kaniini. The project was licensed with LGPL-2.0 and they changed it to MIT, which LGPL doesn't allow.
Not directly, but it is possible with considerable effort. (many projects, including very large ones) have done relicensing between incompatible licenses before so look at them to see how they did it. QEMU for example did this and they had thousands of active, inactive and unknown contributors.
Now this faggot didn't even try to do it the right way and just unilaterally changed it right away. You can not do that and he deserves all the flak he gets.
His only option is to change it back and then try to do it the correct way.
The correct way differs from project to project, but for say a HUGE project that could involve :
0, DOCUMENT the whole process and what you do!
1, make a best effort attempt to contact every contributor and as their permission for their contributions.
This may be difficult since some authors might not be contactable again. Sometimes your only clue is a generic dead @aol.com address :-(
1.1, people that say NO, their code need to be removed and you need to replace/reimplement it.
2, very small contributions, rule-of-tumb either trivial fixes or changes that are <10-isl lines of code,
if you can not get a response from the author then that is ok. Assume an implicit ok.
3, for large contributions where you can not reach he original author. Talk to legal about how to proceed.
Often they may say well we tried but lets keep it. Keep a prominent note somewhere and IF they reach out and deny the relicensing
then you will have to remove their code and replace it. Worry about that when/if they reach out.
The important part is to make a documented good faith effort to reach the authors and also have a backup plan if they deny the request.
