> What SaaS vendors agree to financial guarantees if they lose user data or have an outage?

Lots of them. See, e.g., https://aws.amazon.com/compute/sla/

Now, they're not written in terms of compensatory or consequential damages, but you will be entitled to a service credit (which is a "financial guarantee" of sorts) if the conditions are met.

Private agreements frequently have these sorts of provisions as well. You need to be a pretty big or strategic customer to get those, though, and they're often paired hand-in-hand with long-term agreements with mandatory minimum spend.