That’s right, the only way the network would converge back on a single chaintip without intervention would be if the soft forking chaintip outpaced the non-enforcing chaintip and the non-enforcing nodes reorged to the soft fork chaintip. 

This is highly unlikely when only a minority of the hashrate enforces the soft fork.

Murch

bitcoin

A soft fork is a 51% attack on Bitcoin

Scoresby

*To be honest, I find this stuff difficult to reason about, so here's my best guess:*

If a soft fork doesn't have majority hash power enforcing it

and if a block gets mined containing a transaction that is invalid according to new rules

miners running new rules won't build on that block

If majority of hash power *will* build on that block

chain will split

and miners and nodes enforcing new rules will fork off from rest of chain

I don't see how the soft fork side of the split is ever reconnected with old rules side. 