That is a hard question to answer as, we only know what was in the media. But perhaps RBR had other plans, of which the press was never made aware of. There were many things going on inside RBR at that moment. Like the switch to Honda for instance, which could of course have had massive consequences (rumours that Honda wanted to have a Japanese driver....).
But based on what happened inside the RBR with his seat I don't think RBR had any plans to replace Ricciardo at that time. So from sportive point of view I think she should have accepted to become the second driver as he would currently have been in a better car.
However I think his transfers to Renault/Alpine and McLaren made him quite some money, so I don't know whether staying would have been the right move from financial point of view.
Cheers,
Huub