Why would you want to no longer have a personal backup of your own? Storage is cheap nowadays. Even if you don't use time machine you should always back up.
If your machine dies, it is really simple to restore form a backup. And if your only talking about your music library, well it will be much quicker and simplerly than trying to download the lot again, assuming all the tracks remain available. Plus what about other stuff in your library. Movies etc?
I believe having a cloud backup away from your house is good (in the event of fire/theft/disaster), and having a backup in your possession is good in the even of cloud service backup fails.
Most cloud services will not accept responciablilty for data loss in event they have a failure.