1. You are still liable for the advance non canceleable rooms date and room rate whether your CC can be charged or not

advance rate terms are unequivocal, ie are not "advance rate non cancel only if my CC has available funds or is not closed"

booking a new lower rate with valid CC is very much not in spirit and hotel is entitled to take a dim view of such shenaigans and charge new CC suplied against first booked room with invalid card

2. If rate comes down AND you book a second advance rate non-cancel room supplying a different valid card, hotel would not be outside the law to charge both rooms to that newly supplied CC

what typically happens is one of
a)hotel is low occupancy can not resell room so hotel honous your res at on-the-day checkin time at whch timeyou can pay with valid CC
b)hotel is high occupancy/oversold sells your room at a higher rate
c)if hotel sells room, no rooms left, or only different categories left, and you turn up, hotel can ask you to pay rack rate on available categoruies
d)if you don't appear, hotel could just inform IHG corporate who in theory will not pay hotel BUT will cll cancel your elite status/account/points-balance