It would be so fascinating to know what the world would've looked like had Miriel not died, or had she returned from the Halls of Mandos and lived among her kin again. Because I think she would've moved some big pieces, one way or another (well, she kind of already did by the choices she did make, but anyway)
I wonder if we tend to get a mental picture of Miriel as the poor, frail mother who was so exhausted after making a son that she had to flit off to the Halls of Mandos, or just sit around passively forever. But in all honesty, that's kind of inaccurate.
Somewhere in the legendarium, it's said that Fëanor resembled Finwë in appearance, but in temperament he was more like Miriel. And what do we know about Miriel's temperament? She was stubborn. The more they bugged her about coming back to life, the more obstinately she refused, just because they kept bothering her about it.
Fëanor possibly idolizes his dead mother, but he also possibly romanticizes the concept of her because she's dead. But in a world where she had come back, they would've been an explosion duo. Either Miriel would've made Fëanor worse, or they would've butted heads so hard the whole world would've spontaneously combusted.
Or maybe some of both. Maybe Miriel would have nurtured and encouraged some of Fëanor's traits early on, feeding his stubbornness while it was still largely a good thing. The whole time, she was helping create this immovable force. But then, when Fëanor started making certain decisions, and if Miriel didn't agree with the direction he was taking, then they'd find themselves on opposite sides of the Oath, and hoo boy! There'd be more than just ships burning!
Or! Or! Alternatively, consider a world where Miriel took sides with Morgoth. A world where Morgoth has Miriel as an ally. A world where Fëanor yells, "Get thee gone from my gates!" And Miriel says, "Haha, just try to get me gone from your gates! The more you yell, the longer I'll stay!" But of course, Fëanor can never bring himself to kill or harm her, because she's his mother.
But I mean, what would a Miriel vampire be like? Or a Miriel werewolf? A Miriel orc? Terrifying.
No, she doesn't have the fiery spirit Fëanor has, but it seems like her stubbornness could make her capable of an awful lot of trouble. Long story short, the world was a safer place with Miriel sequestered away.