Permanent alimony is only awarded in 7 US states, and I know that at least in one of those, NJ, it's certainly not guaranteed and can be negotiated around. In the state I'm getting a divorce in and the state I'm currently living in the cap is 1/2 the term of the marriage.
Additionally divorce is a complex process that is largely about handling the cases where the two parties cannot agree. If both parties agree a divorce can be finished in an afternoon and the outcome can be whatever both parties agree to pay. But even in a highly contested divorce there is still a lot of room for negotiation. Even in states that allow permanent alimony this can be negotiated. It's pretty rare that your divorce won't settle before the final court date.
Furthermore, even if your ex-spouse is awarded permanent alimony, you can always go back to court if your earnings is severely limited. No court in the world is going to make you pay alimony based on a $100k income if you end up being forced to make $40k.