Yes, this is a risk. When you deposit coins to any exchange, casino, mixer, etc., then you are giving up custody of them. This is a risk I am willing to accept with ChipMixer due to a number of reasons: Firstly, I am mixing small amounts of coins at a time and not leaving amounts I can't afford to lose in the custody of a mixer, and secondly, they have mixed hundreds of thousands of bitcoin over the years without a single incident of loss or theft.
I am sure someone will create a way to reduce the risk soon, maybe something similar like Bisq is doing but used for mixing of coins, like you mentioned before.
Maybe we should all start thinking out of the box for solving this problem.
Is it possible to use something similar to a smart-contract for this? I understand that this is not ETH and there is no such feature on the BTC network.
But what if something similar is applied?
User sends BTC from address 1 to mixer. At this point, a smart-contract is created on the ETH network (or any other, on the basis of which it can be implemented), equivalent amount (in ETH) sent by user BTC is frozen.
The conditions will be as follows:
1 - if user receives BTC at the address 2, then the deposit from the smart-contract is returned to mixer.
2- if user didn't receives BTC at the address 2 after the allotted time, then the user receives a deposit from the smart-contract in ETH.
In the worst case scenario, the user lost BTC, but gained ETH, the equivalent of $. If desired, user will be able to exchange ETH for BTC in some exchanger. Yes, there will be partial losses, but this is not a loss of 100% of the amount sent from address 1.
Also, all this will create additional costs (for example, the same commissions for transactions), which will ultimately affect the end user.
I don't pretend to be a genius idea (quite the contrary), but there is such a cool thing as smart-contracts that can possibly solve the trust problem, including with mixers. If it is impossible to implement a mechanism to protect the user from losing he's BTC when interacting with mixers, on its basis, then why not take advantage of the possibilities of other technologies?
Firstly, I am mixing small amounts of coins at a time and not leaving amounts I can't afford to lose in the custody of a mixer,
The issue of trust (reliability) to mixers would also save users from such unnecessary actions. Why send in parts of 10 transactions when you can send the entire amount you need in a "couple of clicks".
This can also reduce the unnecessary operational burden from mixers (they will still receive the same commission as from one large transaction or many small ones, but for the same amount), therefore, the issue of trust for them also remains relevant.