I'd distinguish between small and large communities. For example, if the World of Warcraft subreddit implodes somehow it's basically guaranteed that another one will arise, although you do often get awkward userbase splits, eg. /r/gameofthrones vs. /r/freefolk. I'd say that basically any community with 100k members will continue onwards from a mod implosion.

For smaller communities (<10k members), it's probable that reformation would not happen in a clear way if a founding mod destroyed it, unless the community is booming.

For communities in the 10k-100k range, I could see things going either way.