Yes. Companies with existing workforces are doing new software all the time. If you have a workforce with let us say 100 devs. Even if you hire 10 new ones temp

Yes. Companies with existing workforces are doing new software all the time. If you have a workforce with let us say 100 devs. Even if you hire 10 new ones temporarily or permanent, you for sure tell them: use what the other 100 do. It is not maintenance what drives this, it is the lack of momentum in your work force. And that is very okay. (Modern) Java and .NET are excellent choices. There is nothing wrong with them.