As sibling comment mentioned, depends on if you integrate with those protocols whether or not you are exposed to external security issues. As for upgrades, som

As sibling comment mentioned, depends on if you integrate with those protocols whether or not you are exposed to external security issues. As for upgrades, some protocols are immutable and can't be updated, however, most complex protocols implement some kind of upgrade mechanic. Smart contracts cannot change their code once deployed, but you can implement a proxy pattern that delegates calls to an implementation contract, and swap out implementation contracts as needed by updating the pointer on the proxy. Some protocols have simple single owner systems for updating the implementation. Some are owned by multisigs and may require a 5 of 9 (or whataver arbitrary majority configuration) committee to sign off on the upgrade. Others require a vote by the token holders of the protocol to approve an upgrade. If it's an upgradeable protocol then it can be EOLed, otherwise it lives forever onchain.