ATC might be telling you climb to 5000ft VISUAL for a number of reasons.
1. To ask you to sight another aircraft passing at some later time.
2. ATC may not otherwise be able to track you on the 090 heading unless you do remain visual & like the post above states responsible for your own terrain separation.
3. The 090 heading may be towards higher terrain (read above you) but he/she may intend to turn you prior to that terrain.
If terrain is a problem & the old VHF's fail after accepting the clearance, ATC may have had you tracking towards the said terrain & would assume you are visual with the terrain in sight.
If you can't abide by the requirement to remain VISUAL then simply tell ATC unable.