I'm sure I'm about to open a can of worms here, but the answer is....Maybe.
There was a time when TV Dinners were cheap imitations of food that did nothing but harm for us.
However, thanks to the current trends in nutrition and health, this has changed. There are several brands of frozen entrees that you can eat on a regular basis and get by perfectly fine on. Can you survive off of nothing but these? Probably not, but you said "mostly" not "completely" so as long as you supplemented those entrees with whatever nutrients you might be missing, as well as a good vitamin regimen (which you should have no matter what you eat), then yes you can be healthy.
As a matter of fact, even some diet plans such as Weight Watchers and the P90X nutrition plan suggest certain frozen entrees.
Myth #2 - frozen vegetables.
The masses will tell you "ZOMG! DON'T EAT FROZEN VEGETABLES THEY LACK NUTRIENTS."
This is false. It has been proven otherwise. Being frozen does *not* harm these nutrients. As a matter of fact, some say that this is BETTER than eating fresh produce. Frozen produce tends to come right out of the crops, and flash frozen. Fresh produce is picked, sorted, shipped, and put on shelves waiting for you to buy it. THEN it sits around even longer waiting for you to eat it. During this entire downtime, nutrients are breaking down and degrading.
I myself prefer fresh produce, for a number of reasons which have nothing to do with this topic - so I have no reason to explain this aside from it being truth - but as far as health is concerned, frozen veggies may be the best way to go.