So there's this mod I absolutely adore the concept of, Grace - https://www.curseforge.com/minecraft/mc-mods/grace - it allows the player to be given a second chance when being dealt lethal damage during the Enderdragon fight, and it also tickles that little Undertale neuron as well. A mod like this would be AMAZING to have on Fabric with all the Enderdragon fight overhaul mods out there.
A bonus reason for Fabric, but not required would be considered implementing compatibility with the Undertale Death Screen mod, with the heart splitting before quickly refusing back together.