Heatshields running out of ablator has no effect on their skin temperature resistance or conduction to craft internals.

[njits23]

Back when Deadly Reentry was still working, it was the way by which the subjects of the title were managed in RO.
However, now you can reenter from LEO using a heatshield completely drained of ablator with zero issues, as all the ablator does is provide additional cooling, and the skin temp without the ablator never rises above the maximum skin temp of the heatshield.

Perhaps Deadly Reentry should be fixed to work on the current version of the game, or the portion of DeadlyReentry responsible for ablator behaviour ported to RO: https://github.com/KSP-RO/DeadlyReentry/blob/16c997e37c110763c74bcf83b3ad44b96ebbd6da/Source/DeadlyReentry.cs#L829