i think the true answer is, "it's impossible to know". a loss of that magnitude would wipe out alot of Bitcoin's most ardent supporters, eliminate the perception of SOV, and could set the community back 100 yrs. in that sense, the BTC price could tank. i know i wouldn't trust crypto devs anymore in my lifetime if i lost scBTC from that scenario. or, yes, it could "make all our BTC more valuable!" that's certainly the conventional thinking around here.
the difference with your gold example is that i doubt the Chinese had any idea a Spanish armada ship laden with gold went to the bottom of the Atlantic. today, we have the internet and the media would be all over it.
that's a fair statement but again, how does sidechain increase the risks of BTCs being lost to centralized, malicious or corrupted scheme?
If the notion is that: "Side Chains are great because people more foolish than I am will mistakenly trust some bad ones, and use them, and lose some of their coins making mine more valuable."
Than this isn't particularly good for Bitcoin if people lose confidence in it, so whether it may or may not be good for one's own bitcoin value is questionable.
Here is one scenario where BTCs may be lost to MC in this way, essentially rendered unspendable through an economic activity.
1) Some BTC is SPV'd to scBTC
1.
2) Some scBTC
1 is SPV'd to scBTC
2.
3) scBTC
1 is discovered to be a scam (or just a bad implementation) whereas scBTC
1coin massively inflates so that no one on scBTC
2 has any incentive to SPV back from scBTC
2 to scBTC
1 and so no way to return to MC.
(Yes, you can create a side chain from a side chain.)
complexity risks...
Edit: Is there a way to have such an event without sidechains, or is this a "new" risk?
well essentially you're suggesting the coins were initially transferred to a non-secure scheme without proper due diligence from the owner so my answer is no, this is not a "new" risk.