https://etherscan.io/token/0x1a95b271b0535d15fa49932daba31ba612b52946
Yes the circulating supply will still be thesame, but if you send your BTC to Bcash address you have just burnt that BTC but it is still in circulation but can't be spent.
This is not true. BTC and BCash is different networks working with the same address generating algorithm, if you send BTC to "BCash" address, the BTC will arrive to BTC address, which looks like the same as the BCash address. There is nothing about burn.
About MNE supply, and burning. The contract the 568k MNE sent to does not have selfdestruction method, nor any sending deny method, so as I see, yes, those MNEs could be spend again id dev want it.