If you RW project files are on a disk that is set to backup in Time Machine then yes, they are being backed up. (Check Time Machine setup). I'm guessing your files are on your built in hard drive and if you are using time machine then they are being backed up. You should go into TM now and learn how to find them and restore them so you know what to do if you lose them.
Now, what if your Mac crashes? Then you should have external copies. This can be to external drive or cloud (iCloud, dropbox,etc.) (working on RW project files while they are in "the cloud" is not recommended). I use Dropbox and sync to my other two computers. I also use Carbon Copy Cloner to copy my RW project files to external disk each night. I do this so I can keep 7 copies so I can go back to any day over the past week and restore.
What if you need to work on RW while traveling and you have a laptop? (I mainly use desktop iMac but have a MacBook Pro too) Make sure current copies are in the cloud so you can use them on the road.
What if you have a fire or theft and your home setup is completely lost? I have a pocket drive that contains a complete system clone. When I leave the house I carry this drive with me in the car. Should my house burn I can run to the store, buy another iMac, connect my pocket drive to it and be up and running EXACTLY AS I WAS, with all files current, just by connecting the clone drive.
Lesson... there are different kinds of backups for differnent situation. If you have backups, the "other" thing will happen so make sure you are backed up completely.