It will last as long as they make a profit. Then, they will have to bring out a new vaccine for a new covid.
Worth noting that Astra Zeneca are producing their vaccine on an at-cost basis, and have said they will continue to do so until the pandemic is declared over. This, coupled with the fact that it can be transported and stored at normal temperatures, rather than the extremes required by Pfizer etc, means that outside the US the AZ is selling at about $3 a shot, compared with eg Moderna $35.