Myrkul has yet to be addressed.
He was brought back along a lots of other dead gods at the same time when the 5e timeline started. I don't think WoTC has any interest in explaining how, they just wanted to reset things to pre-Time of Troubles with the pantheon.
Larian may be playing fast and loose with the lore in BG III -> the stuff with drow eyes, how mithral is made, now this with the Paladins-but 5e is a notably very lore-adverse edition. I doubt WoTC care too much about the 'details' as long as Larian hits the right bullet points. Bullet points that sometimes contradict major parts of established realmslore anyways.
The Paladin stuff has WoTC all over it to me, there are plenty of indication since moving to the 5e timeline that WoTC don't want the gods anywhere near the players. I wouldn't even be surprised if the Lolth and Tyr interactions were removed for release.
And the change in the early access is recent. There are still dialogue tags for Paladins in the game files and the deity selection is only hidden in the UI in patch 9. The Paladin dialogues sometimes default to a deity one too:
- with Anders you're a paladin of Tyr
- with the Druid you follow Sylvanus
- with Wyll you refer to a "she" as your goddess
The Paladin in BG3 is currently a charlatan, it should stick to Oathbreaker.
