There are no plans for deactivation today, but it might change in future. Bitcoin is meant to be trustless, so Im not going to store Bitcoin long term with SegWit transaction, because I would need to trust another Soft Fork wont deactivate the use of withness part where signatures are checked. No FUD, just rational from my part as I will be using SegWit transactions only for hot wallet and low amounts, not for a cold longterm storage.
You can use the witness outputs nested in a p2sh output (the kind of address that segwit wallets will be creating). The witness output scripts act as the redeemscript of the p2sh address, and because that is hashed, no one will be able to spend your coins even if for some reason a soft fork happened which deactivates segwit.
This is an irrational fear and not a particularly valid one because segwit fixes the transaction malleability problem, and deactivating it would simply reintroduce the issue, something that no one wants to happen.