Dropped seat selection, help!!

Hi all, been following this forum for tips for awhile now, and now unfrotuantely have come across issues of my own.
I have a rewards booking on VS900 in PE this Friday (Class P), returning on 15th April on VS901 NRT-LHR in Economy (Class T).
I recently noticed that my return flight disappeared from Manage My Booking online. Called and was told that when I accepted a flight time change online 5 months ago, a system glith dropped my flight. It's since been added back, but my seat selection has been dropped!! When I check now, there are only 4 seats left in all of Economy and they're all terrible choices, last rows in the middle of 4. The operator says the flight may be overbooked and to wait for online check-in 24hrs before my return flight, as 40% of the aircraft will open up for seating and there should be better choices.
Is this true? Or will I run the risk of an overbooked flight and not have a seat at all? Should I just take one of the crappy seats now for safety?
Not very happy about this situation at all, especially as I am travelling with a friend and his reservation/seat selection is all fine. I've now lost my original seat next to his.
!
Thanks for your help in advance
I have a rewards booking on VS900 in PE this Friday (Class P), returning on 15th April on VS901 NRT-LHR in Economy (Class T).
I recently noticed that my return flight disappeared from Manage My Booking online. Called and was told that when I accepted a flight time change online 5 months ago, a system glith dropped my flight. It's since been added back, but my seat selection has been dropped!! When I check now, there are only 4 seats left in all of Economy and they're all terrible choices, last rows in the middle of 4. The operator says the flight may be overbooked and to wait for online check-in 24hrs before my return flight, as 40% of the aircraft will open up for seating and there should be better choices.
Is this true? Or will I run the risk of an overbooked flight and not have a seat at all? Should I just take one of the crappy seats now for safety?
Not very happy about this situation at all, especially as I am travelling with a friend and his reservation/seat selection is all fine. I've now lost my original seat next to his.

Thanks for your help in advance