Runtime errors themselves generally won't crash the game outright, unless they happen somewhere like world/New().

A runtime error just crashes the proc that causes it, causing it not to continue beyond that point. This can cause a chain reaction if you have things that rely on that proc finishing.

There's also a different kind of error that presents like a runtime error but isn't actually the same. Which is an infinite loop, these generally happen when a proc loops quicker than the game can keep up. These kinds of things are usually where your crashes and excessive "lag" come from.