Is it permissible for the butcher to dispose of the sacrificial animal he was entrusted to slaughter and sell it to another, then buy a new sacrificial animal and present it to the sacrificer without informing him, due to the sacrificer's delay in receiving it and the fear of the old sacrificial animal spoiling?

What you did by selling the sacrificial animal is forbidden and involves two transgressions: The first is that selling the sacrificial animal is forbidden, and the second is that you defrauded the second buyer and corrupted his act of worship. Therefore, it is obligatory for you to compensate him with a live sheep similar to his sheep. As for your compensation of the first buyer with another sheep, if you slaughtered it for him with the intention of sacrifice, then there is no harm. Otherwise, you are obliged to compensate him with a sheep.