Replacement Crew
There was a crew scheduled to come to replace Krikalev and Artsebarsky in October. However, the engineer who was supposed to take over for Krikalev didn’t have enough training for a long stay in space.
Source: scribol.com
Due to the situation that July, Krikalev agreed to extend his stay on Mir. The relief crew still took off in mid-October 1991 but, not to replace Krikalev.