I had something similar happen, where I made a points reservation and then a fix up of a previous accounting glitch put my account into negative. The result was that a couple days later that reservation was cancelled. Lucky I was able to rebook at the same rate for a shorter stay.

I don’t suggest you make that new booking unless you don’t mind it getting cancelled on you with no warning.

That said, in general if you have a negative balance and just don’t use the account, they won’t go after you. Somewhere in the T&C the points are defined to have no cash value. But if you are titanium, I’m guessing you will replenish your balance soon enough.