Rotary magazine models were offered right up to the end of production. There was no change, the detatchable mag models were an addition to the line, not a replacement.
Not sure the precise date, early 60s I think, but might be later 50s, when the "clip" model 99s first show up.
Savage never abandoned the rotary magazine. Original 1899s and Model 99s had bronze carriers, changed to brass in the 1960s, then changed to steel, and finally to aluminum. The rotary magazines were available until the end of production for the 99.