The fact that those apps are still 32-bit means they're unmaintained. The fact that they're unmaintained means that they're likely to break at some arbitrary OS update anyway. Even common apps like Tweetbot, by reputable developers, will break on a new major version, so your app that hasn't been updated in years is probably going to die off soon anyway.
The only way to make sure to keep those apps open is to keep from updating iOS, and if you do that this doesn't affect you anyway.
There's no reason apps should break on arbitrary OS updates as long as they are well-behaved and stick to documented UIKit APIs and so on. I have apps from 2009 that work perfectly well for the task they need to do. The companies have long since folded and closed down their app store account. Others have similar apps, perhaps controlling $1000+ worth of DVR equipment. I think (and hope) Apple may be underestimating the effect of a vocal minority still requiring these apps, and the chilling effect this may have on paid apps or even free apps for the made-for-iphone hardware program in the app store in general.
And a lot of games hardly even use UIKit, relying only on OpenGL ES and some input handling logic: these are the kinds of apps I would expect to essentially never break (and would usually assume a platform bug if they did break).
I run iOS public betas and many games break during the beta period of new iOS versions. Even highly-rated apps like Rayman Run has been completely broken for weeks for me; like the audio breaks out, the touch input is not accepted in some menus, etc. At some point I couldn't event start the game. Then, an update arrives and everything is fine.
The only way to make sure to keep those apps open is to keep from updating iOS, and if you do that this doesn't affect you anyway.