I think the burst altitude is far more related to how full the balloon was. Fill the balloon a lot and you get a fast ascent but a lower burst, underfill and you'll get higher for the same payload weight, but of course you get blown further.
It seems like extending the operating life of the device is ideal since then it could tolerate a much slower descent and burst much higher.
On #highaltitude, what were the highest altitudes others have achieved?
I believe the record is just > 40km
You could design a two balloon system with a secondary balloon that is nearly initially empty that will take over lift after the first bursts.
Or an automated valve controlled by a manometer. The people who build these awesome contraptions seem to put a lot of effort into the payload and comparatively a lot less into the balloon.
The design goal isn't usually to maximize time at altitude. If you do that, your balloon lands 10,000km away and is difficult to retrieve.
But a common design goal is to maximize altitude, and an automated valve would help with that. You can also have it wired to open if the balloon stops ascending, or strays too far.