But why would they extend the LCY-BSL route to BRN if not for replacing SEN-BRN with it? If the new rote was only meant to replace the long-existing LX service on LCY-BSL, there is no reason to overnight the aircraft in BRN, particularly as it is a wet-leased aircraft anyway. And serving to Londo airports from BRN makes even less sense as the high yield traffic from BRN will most likely use the LCY service, further diluting the yields for BRN-SEN.
The only hope I see for SEN-BRN is that it quickly turns out that the demand from BSL and BRN combined is bigger than 100 seats daily offered with a combined Saab 2000 operation. Swiss used to offer more than 200 seats daily alone to BSL until last week. So the overall capacity goes down from 280 seats to just 100 (of course some Swiss pax will simply continue to use them from ZRH now instead of switching to Skywork, but anyway). But even if that happens, the question is of course if a more logical solution would be to simply add additional flights from LCY to BSL/BRN to offer a more attractive overall schedule - or two move the separate SEN-BRN flight back to LCY (less likley IMHO).