Recently, a local paper had a terrible story: two degenerates broke into a mausoleum , looking for gold/jewelry. This tomb was last opened in 1889.
I know that the old horror movies depict these things as full of cobwebs with dust on everything. But would it? With no entry way, there would be nothing for spiders to feed on. As for dust, once the doors were sealed and locked, nothing could get in.
It was also noted that this tomb had solid bronze doors-thieves have been stealing ccopper and bronze now (because the price of copper has tripled).
I think we will see a lot of such vandalism in the future.
I would think that there would be a small vent in the mausoleum.
There used to be a problem with people stealing Tiffany windows from mausoleums in my neck of the woods.
It likely depends on the difference between “sealed” and “completely, utterly airtight”. The former is quite plausible; the latter seems far less likely (especially in a structure that old). Spiders and insects would need no more than very tiny cracks or holes to make their way inside.