I don't have answers to all of your questions, and I suspect the answers may be changing with the Obamacare exchanges coming into play. In the past it may have been difficult in some cases to opt out of company health plans entirely and then opt in later, but I believe with the latest Obamacare changes they cannot exclude pre-existing conditions and I expect that would also mean you could opt in later. However this is all speculation on my part, look up the info. or ask your (spouse's) employer for their answer.
I am using a HDHP and HSA, however that is offered to me through my employer, so I did not have your issue of wondering whether I could switch back--in open enrollment every year I could elect any plan. The premiums are much lower than the traditional managed care plans, and my employer also puts some money into the HSA for me every year.
I switched to the HDHP/HSA about 2 years ago and I think it's been a great decision. My two kids, DW and I are all in good health so we haven't had a huge amount of health expenses. We have a good income so we pay everything out of pocket, and have not made any withdrawals from the HSA--I am trying to keep all the health related receipts so that eventually I can make claims against them. As I understand the rules there is no expiration date on submitting claims--so 20 years from now, I can submit claims from today and get that money out tax free. Assuming no health catastrophes, I plan to use the rest as another retirement fund.
When I made the decision to change, I did the math on the various scenarios. The HDHP is all out of pocket (or HSA-reimbursed) up to the deductible, and then essentially everything is covered 100%. With the various managed care options, there is a co-pay and something like 80% coverage of most other things IIRC. When I did the math, if we were all healthy, we won by being able to pocket the difference. If we had some major catastrophe that cost something like $100,000 or $200,000, the HDHP would also win since beyond the deductible, everything was covered 100%. There was a small range near the top of the deductible where the managed care option would be cheaper--*for that year*. But if you looked at several years in a row, if there wasn't some sort of chronic treatment going on, the HDHP/HSA would still win.
Seemed to me it was a no brainer as long as I could afford to pay as I went for health care up front. If I was just scraping by then I could see the argument for the managed care option, to essentially make your costs more predictable and spread out over time (but it would cost more!).
Perhaps there are scenarios I didn't consider, and you would certainly want to understand the specific costs and terms of your plan options. Just thought I'd share my experience with it.