This assumes the game isn't designed from the beginning to be entirely reliant on the operation of servers. For instance there never has been and never will be any form of offline function for Destiny 1 or 2, even if all the person wants to do is play the single player campaigns.
Destiny 1 partially ran on consoles, though. It was mostly p2p: https://gist.github.com/nessus42/55c1260d88e2028689de0c49381...
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Do we know any of the technical details of that? Is the SPC just instanced multiplayer with all game logic on the server, or is it just getting some encryption key?
First, SPC, at least in Destiny 2, required you to do Strikes. Second, you get item drops. Technically there is no SPC in either Destiny because it's an MMORPG. There are just plenty of things you can do all by yourself and things that you meant to do alone, and those things usually come with item farming, so you need server-side to make it fair.