There is no perfect solution. Either the data is completely secure, and can easily become unretrievable, or it's just barely secure, and easy to recover, or somewhere in between.
Since the compromise depends on a lot of subjective factors, I can't even offer good advice on that.
Personally, for my own secure data, I have a pattern of passwords/keys that I use. They are strong passwords, but I only rarely change them. Studies by the NSA and various universities and such have actually shown that routinely changing passwords causes a net reduction in security over time, because of the very factors you're dealing with here. The "change your password every X days" rules create the illusion of security while reducing its actuality.
- Gus "GSquared", RSVP, OODA, MAP, NMVP, FAQ, SAT, SQL, DNA, RNA, UOI, IOU, AM, PM, AD, BC, BCE, USA, UN, CF, ROFL, LOL, ETC
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"Nobody knows the age of the human race, but everyone agrees it's old enough to know better." - Anon