Oman Air has cancelled all European routes until March 31, except London and Frankfurt. On the Manchester route they are heavily reliant on transfers to India and Pakistan, so until those markets reopen for non-direct traffic, there is no point operating. As far as I know, they were not planning on dropping the route. They seemed happy with its performance and it was rumoured there would be an upgrade to 10 weekly in 2021, but a lot depends on what the carrier looks like post covid.