You don't always need a missed block, but if you do, there are alternative paths to aquire missed data.
So, how do you know that you missed a needed block?
Double/tripple/etc broadcasting does not solve the problem. When is the block repeated? 8 hours later? What if you are off the grid for 24 hours, or just happen to be off when the rebroadcast occurs. The issue is not "unlikely" the issue is: the system is not 100% guaranteed.
You can retransmit blocks with decreasing frequency as they get older. If you miss recent blocks, wait a little while and you get another copy. If you missed old blocks, you may have to wait a long time to get them, but you will eventually get them.