Longer thoughts:
Letting the vision finish may give Sayaka insights into the things Homura has forgotten, which could be quite useful. However I think it would also traumatize Sayaka, and severely impair Homura's growing friendship with her.
Of particular note, though: we never unlocked Library 3 for Sayaka. I'd thought we'd had a special gift from Sayaka in the initial "missing inventory" stuff (concert tickets or something), but reviewing the missing inventory, there's nothing from Sayaka in there. I must be remembering a different quest.
However, given that, whatever Sayaka's library 3 memory is is likely to be on the unpleasant side. If we have no memory of a time with Sayaka like we do with Kyouko... We do not want Sayaka finishing that sequence. Even if she might conceivably view Homura as a type of 'saint' for the effort she's put in to save Madoka, it just carries too much risk with it.
On the other hand, snapping her out of it risks her only getting half the story — perhaps only the recent time loops, and not the original timelines that gave birth the path that Homura had to walk. Not getting the full story may end with Sayaka reacting badly.
...
Speaking of reacting badly, I just realized the recent pause in posts made me forget to actually select the omake reward. I was still giving serious consideration to Comfortingly Calm. I'm not sure this will quite qualify as Homura delivering the revelation herself, though.
I think.... even if it does not count, I'm still going to take it. I think it fits a bit more with what I hope Homura will become.
[omake bonus] Comfortingly Calm
Also going to go with Wzd_JA's refinement:
[x] Try to snap her out of it.
-[x] Grab Sayaka in a tight hug. You don't know what she saw, but if she saw your "legend"...
