You'll be fine, I'm almost certain of it! Vienna (Bratislava) to Lisbon will probably be in the middle of the night though.
My "man on the ground" informs me one of NE's 737-700s is in Luton at the moment (assume incoming from Poprad then off back to Prague). Is this the first appearance of an NG for months, or have they been sneaking in at other times?