Loki's stocks became safe the moment Oda gave him a legendary fruit that is only second to Nika narrative-wise. *If* Shanks beat him then Shanks is simply that strong and was hiding his full strenght until Nika is back, not that Loki is weak.
Only way he won't be a major player in the final saga is if he's die this arc, but considering Oda been hinting a relationship with Shirahoshi I doubt it's happening.