Still Valid
As far as I know, the old pesos are still valid. The last devaluation (if I remember correctly) was a 100-1 change. They chopped two zeros off of all peso notes. I was down in Cabo at the time and it was really confusing at first. Had bills that were 5000 pesos and 50 pesos, 2000 pesos and 20 pesos, etc. Had to look at everything really close until a local told me don't pay any attention to what the bill says on it, just look at the color. Blue is 20, pink is 50, green is 200, etc. Something like that - the colors didn't change, only the amount written on the peso note.
That said, I don't see why a Mexican bank wouldn't take the old peso notes at their current value. Locally, nobody would probably want them. I also suppose it depends on the bank and how many of the old notes you were trying to exchange. But, definitely worth a try.
The most confusing money in the world is (or at least, used to be) Italy. Everything cost about a zillion lire and each bank issued their own lire, so you had these huge wads of different size bills from different banks. Practically needed a wheelbarrow to carry around enough lire to buy anything. I don't know about these days; maybe it's easier there now with the euro, but back in the early 80's, it was insane.