All bitcoins that are not moved for a certain period of time (20, 50, or 100 years) should be presumed lost and then recycled through the usual mining process. I'm not sure if that can be achieved through a soft fork.
If something like that occurs, the whole idea of BTC will be lost
You can hold BTC for years and years and never move any satoshi, and you'll have access to the coins you have
Some move to recycle BTC can create a breach
Satoshi itself said (like LoyceV pointed above) the lost coins can be a donation to BTC