Do termites stay in the wall?
First, let's assume it is subterranean termites...because your post seems to indicate so. The obvious thing I deduce from your desription is that you are not finding termites in those tubes...hence your curiosity about what happens without the tubes. Point 1. Remember that the female worker termites--the one's eating your house--are blind and must have scent trails to find their way back to the colony. Remove those trails and you remove not only their hideaway avenues, you remove trail home for the most part. (But don't let yourself take comfort in that.) Point 2, termites are strictly a colonial organism--no termite exists and lives for itself; so termites living in the wall and dining your house away for their own pleasure is not a concern. 

It is dubious at best what the effectiveness of spot application will be in the long run; and not feasible to think that you can get to them inside the wall cavities. Individual animals you see are only the tip of the proverbial iceberg; it's the hordes you never see (until swarm) that bring down a house quite quickly. 

In most states if not all there is very little you can do but a start would be to inspect and remove any contact between house wood and soil. Next, moisture encourages infestation and invasion so check for sound roof condition, guttering, and any rain paths to the foundation, mud sill, crawl space, etc. Perimeter tiling or drain piping, or water shed ground sloping, to carry water away from the house is another suggestion. 

Ultimately, you will need licensed termite eradication to either inject a barrier or kill the colony with an effective baiting system--most diy systems are not. Barriers work by preventing any temite from getting into the house--because once inside no systemic treatment has been found to be effective. Baiting systems that work, kill the colony by exploiting known termite foraging habits.

One problem with termite infestations--when you see tunnels, or swarms, or specimens (and sometimes ants in large concentration) you know you already have a significant infestation. Another vexing thing about termites is that the longer they have been in your walls, carpet, books and such the faster their rate of destruction... it's never too early to call in the pro's; and time used hoping to avoid the treatment expense by self help is as often as not time spent to the termites'--not your own and not your house's--advantage.