If the 2500 songs are yours (i.e. you bought them) I'd keep them and not replace with Apple Music versions.
Remember that Apple Music (the streaming service) is a "music renting" giving you the right to play the songs as long as the subscription is active. If the subscription is not renewed, the songs aren't playable anymore. You "own" nothing.
At least keep a backup copy of your purchased songs somewhere, even though they are lossy (AAC). They will remain yours, regardless the subscription's status.
I suppose you manage the songs in Music app on a desktop computer (e.g. a Mac). In your Library, in the Songs listed view, the Cloud Status column shows which song is Matched, Uploaded, Purchased or Apple Music.
Matched means that a song you own locally in your library is available in Apple Music's catalogue and so they match.
Uploaded means that a song you own locally in your library isn't listed in Apple Music's catalogue and so it's uploaded on Apple's servers to have it available for streaming.
Purchased means that the song was purchased in iTunes Store.
Apple Music means that the song isn't owned by you because it comes from Apple Music's catalogue and you have added it to your library.