Having your own domain you control the MX record. If google locks you out, you can still move to another host for your email on the same day. You don't get your historical email (unless you backed it up with offlineimap or something like that) but at least you still have access and control over the address. Using @gmail.com for your business (or even personal email) is asking for trouble given how notorious google is at locking people out with no recourse and for mysterious reasons.