Mowbray also confirmed Rovers did not receive an offer for Armstrong in January.
“We want to keep all of our best players," he said.
“I've said that I hope all of our young players re-sign and if they don't, that's part and parcel of football.
“I've used the example of Kieron Dyer when I was at Ipswich, he got sold and the team got promoted the next season.
“You don't want to sell your best players but sometimes there's a necessity, sometimes there's a bid that comes in that you can't turn down, 1) for the club because you can invest the money in other areas of the pitch that might be strengthening and 2) because of the relationship you have with the player and you want them to play at the highest level.
“You must have empathy with your footballers at times yet you hope they have loyalty to the football club that's given them the chance and platform to show their talent.
“Let's wait and see. The phone didn't ring in the January window. He's picked up a little knock, he's got 20 goals, let's hope he can get over 25 goals by the end of the season and let's see what the summer brings."