If miners were to stop mining the difficulty (the computing power needed to mine blocks of transactions) would drop and people like me would start mining. So where did all the existing work go? It went into improving the security of the chain that my mining program is adding blocks to. That basically means that for someone to completely rewrite the provenance of all the bitcoin before the point where miners stopped mining, they’d have to replicate the same amount of work that was originally put into making that history. With less people of ordinary means working on the chain, the security of the blocks generated will be decreased. This is because it would then be easier to launch attacks on the chain and erase history and double spend, but the community could easily be rebuilt to a point where it is no longer feasible for a malicious actor to compete with the miners again.