As long as SAS and other partners need slots filled at Heathrow every route possible run by their affiliates will go that way, unfortunately. So yes when the time comes I expect Kristiansand will go too, if it operates this year at all.
However I think you are looking at the route slightly incorrectly. KRS was the only Wideroe route to London, which as we know was to have transferred to SEN from STN and operated daily. Traffic will be overwhelmingly inbound so the London terminus doesn’t matter that much. BGO only came about quite late in the day last year as a result of Norwegain’s woes. Wideroe had slots at LGW and LCY so the 2x weekly SEN route was something of a bonus probably for the UK leisure market.
So, BGO as a route is only the “big money” in the sense it’s somewhere people in the UK have heard of. I would suggest their longevity connecting BGO to London will come down to how long it is before it’s re-served by a larger airline on bigger aircraft. The core route for Wideroe was KRS, they are predominantly a regional airline and have very few routes outside of Norway. However when the world recovers enough for LHR slots to be relinquished is anyone’s guess and a problem for all other London airports.