asdf1234
I haven't seen any "confirmation that pax numbers will go down and not up over the next 12-15 months". All I recall is Stobart saying a while ago that they expected numbers to be generally flat in the immediate future but that they anticipated continued growth over the next 12 months. I wouldn't rule out a positive announcement in the next week or two which, incidentally, is when Stobart release their interim trading statement.
As you say Stobart have a fully-repairing lease of about 134 years which means the full value of the airport is to their benefit: only when a lease has less than about 80 years to run does its value to the leaseholder decline over time.
There are a number of reasons for the decline in their share price including the fact that they sold 49% of the core road transport operation, so SEN's performance at this stage probably doesn't have much effect in itself one way or the other.
As LTNman says, the Jota 146 will have a negligible effect on SEN revenues but it is still good news to see them expanding.