It’s not up to me, as the GM it’s my job to interpret the players actions and ideas through the lenses of both the rules and the world.

Also we discussed it after it happened and everyone including the player who sacrificed themself wanted the plot to go forward that way.

Why is true resurrection out of range but plane hopping isn’t? This seems like a great opportunity to have them complete a quest for some high level NPC who does have access to true resurrection

There are a few reasons for this that I left out of the post because the context required would have bloated the post, the first is simply that I try to avoid high level spellcaster NPCs because players tend to see them as the solution to everything, the closest thing they have is a wizard friend who studies magic but doesn’t like to use it aside from things like identify.

Secondly the deceased character is from our previous campaign, which soft-ended when that character died because around the same time one of the other players had to leave the group but we got a new player who had never played before who wanted to join, we didn’t want to slap them with an 8th level character sheet though so we started a new campaign with the understanding that around 8th level the two campaigns would converge and the new players character would join the old party. The player with the dead character is fulfilling the role of character who can enable the plane shifting, giving me a convenient way to write the character out when the time comes. The other 2 players will get to choose if they want to continue as their new or old characters. (This was all discussed with the players before starting the new campaign in very big picture terms)

Thirdly, plane hopping just feels more fun to me than standard resurrection and it adds to the weight of the moment. That character died by sacrificing themself. If you’ve played the 5e spelljammer adventure you’d be able to guess exactly how it happened. A running gag of the previous campaign is that no matter what misfortune befell them they’d always weasel their way out of serious consequences (despite my best efforts) and this would be the ultimate no consequences moment.

The backup plan is always just to make it up, but I prefer to stick to established lore with the hopes that 50 years of ironing out (or retconning) has made it internally consistent enough to get by.