Got your PM, I'll answer it here.
Nobody can answer that question with any degree of certainty, because, aviation/life is "dynamic", what seems like a good plan today, can turn out to be cr@p tomorrow.
The "plans" (such as they are ) in all airlines I have worked for have been subject to change, from slight refining, to complete 180degree turns, I doubt that airBaltic is about to buck that trend.
Internally, 737 phase-out date has had more than a few versions already. Impossible to forecast, because the business plan (no matter how well created ) cannot account for outside influences ( another war somewhere, oil prices go sky high, Bombardier offer a sweetener - & the CS uses 22% less - so, Bye Bye Boeing . . . . nobody has a viable crystal ball ) Current offer for DEC /Fastrack 737 Capt position is for 2 years, but, of course they can terminate with the agreed notice period . . . so why get excited beyond 2020 anyhow ? better to worry about the 1 mth notice period if you have to worry about something.