The Flybe booking website currently shows that the SEN ATR routes will be discontinued in February/March. On that basis it looks like the IoM services will use the SEN aircraft. Whether those SEN services (GRQ ,RNS, NQY, CFR) will be resumed in some other way I have no idea.
I think that an earlier statement from about a year ago suggested those SEN ATR operations would only run to February 2020.