As to licensing, Microsoft's "official position" when I last read it is that a motherboard change, in and of itself, invalidates the license that had been for that machine because, effectively, they consider the motherboard the one thing that won't change under normal circumstances.
There is a dispensation in place, that is not difficult to get, if one has to replace one's motherboard secondary to failure. That's a completely different situation than replacing it "just because" or because one is, essentially, building a new computer inside an old case, which is effectively what you've done.
There have been reports here that some people who have purchased retail licenses and when said licenses are linked to their Microsoft accounts, new hardware has been automatically activated because you are allowed to transfer those licenses from machine to machine. In any case, if you reinstall using the license key you had, and they reactivate it then they reactivate it. You've submitted it to their activation process.
But if the Windows 10 instance you had was an OEM installed instance shipped with the machine, it is highly unlikely that it will reactivate, whether linked to your MS Account or not, because that's not a part of the licensing terms. Those licensing terms allow for a motherboard replacement, and I believe only of the same model, if one fails but that's the only circumstance.
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