I think many of the early simple PLDs are obsolete, and have been replaced with more versatile versions.
No. A PLD is just a bunch of logic gates and flip-flops that the user can interconnect as needed. It would replace a bunch of simple TTL logic chips. A microcontroller would not replace a PLD/PLA/PAL.
A PLD/PAL/PLA/FPGA might serve as "glue logic" around a microcontroller or microprocessor.
The "programmable" in these device names may be a bit misleading - I think a better term would be "configurable", and Altera uses that term with their FPGA parts.
FPGAs are configured at power-up (or before, for the EPROM types), and keep the same configuration all the time the system is operating.
A microcontroller or microprocessor continually reads and processes program instructions in normal operations.
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