Unless you're sure they won't work out, why cancel? Delta changes flights often - If they honor this you may be able to change dates if they change flight times on you.
+1
Plus, the reservations were only 250 SkyPesos each. Even if you have 10, that's only 2,500 Pesos, or approximately $0 value
OK fine, it's worth a few $$. But even if you fly on 1 from the speculative, you got your monies worth and then some.