Are there any documented cases of extinction of a species of fungus?
According to the International Union for Conservation of Nature’s Red List there are many endangered fungi, but none that are documented to have become extinct within the time frame of interest to you.

However, it seems likely that some fungi have gone extinct with their plant hosts — according to the IUCN there have been 133 documented extinctions of plant species. In particular, mycorrhizal1 (and other) associations between plants and fungi are prevalent and some of these associations appear to be specific (i.e. the fungus only associates with one plant species). For example, there are reported to be 28 species of fungi that only associate with the shrub Lantana camara.2

References:
1: Hoeksema, J. D., Bever, J. D., Chakraborty, S., Chaudhary, V. B., Gardes, M., Gehring, C. A., ... &amp; Lajeunesse, M. J. (2018). Evolutionary history of plant hosts and fungal symbionts predicts the strength of mycorrhizal mutualism. Communications biology, 1(1), 116.
2: Hawksworth, D. L., &amp; Rossman, A. Y. (1997). Where are all the undescribed fungi?. Phytopathology, 87(9), 888-891.