It probably does not matter where you park the miles. Many FFP programs will expire the miles in 4 years. So if you do not touch the account again in the next four years, the miles will be gone anyway.

For Asia Miles, miles expire 36 months after they are earned, but at least you can redeem for things other than travel (at a premium "price").

In AAdvantage, at least if you have some activities within 18 months, all miles expiration will be extended to 18 months out from the last activity.

In BAEC, again, if you have some activities within 36 months, all miles expiration will be extended to 36 months out from the last activity.

I am not quite sure about JL, but I think it is also 36 months.

Again, all programs expire the miles if you don't touch them in 4 years.