Hello, I am a US citizen and lived in Spain for the past 30 years or so with a valid 5 year NIE which expires in February. At the moment I am in the USA for what may turn out to be an extended stay. Family health issues. I imagine my NIE cannot be renewed from here. I just received an email from my bank ING that my NIE is expiring and that I should send them a copy of the renewed NIE. My question is what happens to my Spanish bank account if my NIE expires?

How about trying to get it sorted at the nearest Spanish embassy or consulate in the USA?

I think Spanish consulates in the UK are able to do that.

Or could you use one of them “gestores” or accountants in Spain, sending all the documentation by post?