Are VOR airways being replaced by RNAV routes as VORs are decommissioned?
Short answer: there seems to be no general plan to replace airways with Q and T routes. The FAA originally proposed replacing them, but the final rule doesn't include it.

You can review the source rulemaking documents in the Federal Register and it looks like the idea of replacing (or retaining) airways seems to have been discarded, possibly in response to comments.
The initial notice suggests that the idea was indeed to replace the airways:

Existing airways, routes, and procedures eventually would be replaced
by RNAV Q (high) and T (low) Routes, and RNAV STARs and DPs.

The proposed rule got some negative feedback on the T and Q route idea from two major industry lobbies:

Comment #20: AOPA and the National Business Aviation Association (NBAA) both expressed support for direct routing and avoiding
excessive implementation of additional T and Q routes.
FAA Response: In the NextGen environment, T and Q routes increase capacity and efficiency while maintaining safety by minimizing impact
to air traffic control. T and Q routes allow controllers to safely
manage air traffic during peak periods and to ensure predictable
transitions between busy traffic areas. T and Q routes overlaid on
existing airways defined by VORs could mitigate potential impacts to
the discontinuance of VOR navigation services.

The final rule has only one mention of airways, and doesn't mention T and Q routes at all:

Retain most VORs in the Western U.S. Mountainous Area (WUSMA),
specifically those anchoring Victor airways through high elevation
terrain.

My reading of all that is that the FAA originally intended to move airways to Q and T routes, but dropped the idea after receiving feedback. Or perhaps they just floated the idea to see what the reaction would be.