I've looked at the possibility of returning to the Part 121 world so I can at least share my thought process with you. There are pros and cons with both. The most persuasive reason to return to Part 121 has been, in my mind, a seniority number. If you are furloughed by "Brand X Airlines" and find yourself on the street for 10+ years, unable to find another flying job and working at McDonalds the thinking is that the number itself is worth something. Eventually that airline would recall you and when they do it is their responsibility to re-teach you how to fly.
If you are laid off by "Brand Y Corporate Flight Department" there are likely no recall rights. If you then find yourself on the street for 10+ years, unable to find another flying job and working at McDonalds, there is virtually no chance that anyone will swoop in and restore you to currency. Rather the longer you are on the street, the less marketable you are because you are that much further from the day that you were current and qualified.
Also, unlike most Part 121 carriers, these furloughs may occur out of seniority. That in and of itself is not an issue except that the older one gets, the harder to compete with the young folks for work. So if you are let go at 40...45...50 what is the likelihood that you would find work flying again?
All that said, Part 91 has many advantages. There are relatively few TSA hassles. I fly about 1/3rd as much per year as my Part 121 major airline colleagues for roughly the same pay. There are bonuses, stock grants (vs options), and the ability to collect hotel points (which really do add up, especially when you sign up for promotions). I like being able to rent a car on overnights and see the places we visit. Not long ago I posted some photos of a day trip we took to Area 51... last week I spent the day with my parents... yesterday I was kayaking in Maine. There is more flexibility to get time off for special life-events because you're not just a number. If you work hard, you are often rewarded. No hat, no tie, no stripes. The airplanes are always in pristine condition... any MELs are extremely rare. Most FBOs are far nicer places to spend the day than most airline crew-rooms I've visited. It's pretty rare to be working over Thanksgiving, Christmas, July 4th, etc... (the boss doesn't want to be away from home any more than you do) It's a terrific job -- more fun than I ever had doing out and backs to LaGarbage or sitting in the Conga line at Philly.
So when I was comparing the two I was using financial and lifestyle analysis.
1. Any 121 job will be a paycut -- at least for a while. How long will it take me to get back to my current level of compensation?
2. Then, how long will it take me to make up for the loss sustained during #1
3. Projecting out, what is the difference in pay over the remainder of my career
4. Does #3 offset possible decreases in quality of life associated with commuting, reserve, etc.
The problem is that very few airlines these days pass #2 and #3. As the airline industry further consolidates the choices are fewer and farther between. I have friends at LCCs and startups who love their jobs, but it would be financially irresponsible for me to pursue a career there .... unless I were to lose my current job. Even at the majors the numbers really don't work except for a few, and then only if you consider upgrade a possibility which, for most, is a pretty long timeframe. And then there is the unpleasant reality that even if I find one that I would be willing to leave for... getting the job has proven to be a challenge. I've had a few interviews, but none successful.
I would recommend Part 91 to anyone, it's truly a blast! But as a person who has been unemployed in aviation a time or two (or four) when I was younger, I can't help but to imagine going through the same thing as I get older -- and now with a family to feed. Scares the heck out of me.