If Eurowings takover Brussels and we lose BM outright, we'll be worse off...
If they swap BRU for FRA/MUC, we'll be better off
6 weekly BRU would probably still work out for business. Hypothetically, £300 return with BM, or £50-100 return with BM and 1 night in a hotel, for business there might not be any difference.
As you mentione, it would open up BRU more to city breaks, and I would hope a return to 2 daily might be a thought in their head down the line, although it's debatable whether we could support it. I think with low fares maybe we could.
I'm sure FRA/MUC link would be better off for business and connecting traffic than BRU (except people who want to be in BRU - which will probably reduce come Brexit and the market demograpics of NCL-BRU will change)