we believe someone accidentally removed several fields from a custom form, where can i see the change history of this?

Custom Transaction Form > History (tab)

The consequences of that are one of the worst things about NetSuite. Fields not getting set & silently failing because of it

Agreed. One of the things I was shocked to learn was that the SOAP APIs reference these forms and are impacted by user facing forms being hidden/disabled. And you won't even get errors. Fields values just won't get set. If you are doing any type of Web Service integrations, you cannot safely allow users that aren't familiar with those integrations to edit forms.

I must admit, it bit me when I first started using netsuite. Removed a load of stuff from a form that the users really don't need to see, hilarity ensued. Totally didn't expect it, as it's so dumb

Same, same. 🙂

It's one of the first things I now tell NS admin/dev newbies that I work with

thanks guys!