If you look at steemd.com you can see on the top right the current value of MVests.

Basically your Steem Power is actually made up of your Vests but it appears on steemit as the Value in STEEM. If you stop receiving rewards for your posts or curation the amount of vests you have stays the same. But even if you went away from steem for a week the amount of Steem Power would have grown because the value of your vests (in steem) is constantly increasing.