is it possible to upgrade for this unconfirmed tsx to segWit-Bech32?
No. You have to create a brand new segwit wallet and move all your coins to it to take advantage of the lower fees segwit provides.
am i need to wait 679494 blocks if its unconfirmed?
No. The locktime is the earliest block which can include your transaction. Since we have already passed block 679,494, your transaction is free to be included in a block.
how many days should i wait for dropping from mempool if my tsx still unconfirmed
Provided you do not rebroadcast your transaction, it will be removed from default mempools either when the mempool size limit is filled with transactions paying a higher fee and your transaction is purged from the bottom, or after 14 days.