Do old FPGA's decay?

I found why my PCTD 3 tape controller was defying my attempts to probe it--the XC2064-50 FPGA seems to be dead as a doornail. Regardless of signal inputs, it remains stubbornly inactive--i.e., my logic analyzer says that none of the identifiable outputs changes state. Since DMA and interrupt logic (as well as configuration) is contained in the FPGA, attempting to read from any I/O port returned FF. A jumper bypassing the FPGA for IO read, shows that the drive status lines are indeed present and readable. Similarly, writing to the appropriate I/O address causes the expected drive line to wiggle. Since I don't need soft configurability (only for IRQ and DMA; the I/O address is set via DIP switch), I may remove the FPGA and substitute some TTL. I haven't decided yet. But do old FPGA's just quietly go belly-up? Or is there something about the XC2064-50 that I'm in the dark about? Are there any easy tests that I can apply to confirm my suspicions? Cheers, Chuck