(a) you have a number to call if it suddenly stops working, and
(b) you can threaten to stop paying them if they don't sort the problem out.
Personally, I use GMail as my main account, and it doesn't worry me that there's some (probably miniscule) risk of being locked out of my account. If anyone wanted to get hold of me, they could still reach me via my work email address, telephone, or Facebook.
I'm slightly more worried that they could lose all my past emails - in which case there would be very little I could do to get any sort of redress from them - but I'm pretty confident that I'm more likely to lose my own data than Google. It is possible to back up your GMail messages to your local machine, and I have taken this precaution, although I don't do this very frequently.