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.
Other than learning how to look for exterior telltale signs of termite damage, such as spent casings and holes in the wood or in the ground, you need to write in a contingency on your offer to purchase for a complete home inspection and/or an additional pest inspection.
As mentioned above in the comments, hire your own home inspector and/or pest control specialist. DO NOT succumb to the pressure of Realtors to use their favorite inspectors. Find inspectors that truly work for the person that hires them, you! If you are not trained in building construction, inspection, or pest control, do not attempt to evaluate the condition of a home on your own.
Some Home Inspectors, such as myself, offer screening inspections. This is a simple walk through (apx 1 hour) and initial evaluation of a house before one even makes an offer. This type of inspection is not as comprehensive as a full inspection that can take 2 to 4 hours in home and documents all the aspects of the house, rather it is an hour spent looking for obvious major flaws or situations that will help you determine if you actually want to consider placing an offer. Once you have found a house you are serious about, this screening inspection is usually much cheaper than a full inspection, but since the inspector should be acting as your advocate, can advise you if there are any major issues that would influence your decision to make an offer or not. For the hundred bucks or so, it can be a huge time saver, allow you to make a more realistic offer, and give you a better feeling of confidence about the home you are making an offer on. Good Luck.
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I doubt it and even if it did, you would have to basically make charcoal out of it to make sure there is nothing "edible" left.
The gold-standard for termite protection is to break ground contact. I'll recommend a concrete or brick "foundation" for your storage rack which could then transition to wood for aesthetics. If you are hyper-sensitive about your wood, use termite guards on top of the masonry before you transition to wood. Termite guards are just steel, usually galvanized, and serve to further make the path from the ground (where the termites live) to the wood (where they eat) more tortuous.