Before you can get your BTC back, you've got to perform burn transaction on the sidechain.
So if the sidechain ceases to function entirely, you have no way to generate the SPV proof that lets you claim your BTC.
http://www.reddit.com/r/IAmA/comments/2k3u97/we_are_bitcoin_sidechain_paper_authors_adam_back/clhpcke
It does effectively mean that a sidechain abandoned by miners may end up costing more in transaction fees to exit than you'd like. The situation is much brighter than being left with altcoins no one wants, and also ignores the possible (likely?) existance of altruistic miners that continue to mine along just because.
But if some implementation of SC (I do not think SC as idea) become scam or there is a bug then bitcoins may be lost.
So in your opinion, does this mean everyone can get their BTC back in the event of a SC failure with just a larger tx fee?
It is very complex to answer.
SideChain can be created in many ways (but obviously you do want to accept this fact)
SideChain(IDEA) is "concept?" what describes your Bitcoin transaction off the main chain (transaction are not recorded in bitcoin blockchain).
One example of sidechain is bitcoin-exchange (one of them is Bitstamp). Bitstamp exists, and Bitstamp creates off-chain bitcoin transaction.(buys/sells bitcoins)
In term of SideChain(IDEA) it is centralized and ONE ENTITY controlled sidechain. -> It exists now.
- you can lock your bitcoins in bitstamp controlled address and trade
- Bitstamp is only miner who creates blockchain (history of trades) . Bitstamp mine transactions -> (who sold/bought, add-to-order-book, market-buy/sell, ... and so on) and Bitstamp publish orderbook.
- and only Bitstamp can unlock your bitcoin (bitstampBTC)
Bitstamp is two-way-peg SC with 1:1 exchange rate and ONE ENTITY controlled sidechain
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Blockstream paper describes how to create different SideChain
- one of them is Federated peg (M of N entities controlled sidechain) -> it can be created without changes to bitcoin protocol now.
- I think, it is better than centralized one
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and finally few variants how to create decentralized (not supported by bitcoin now)
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this decentralized SC can be even combined with (M of N SC's) or (Single Entity SC) in case there is not enough mining power
=> The questions is IF/HOW add decentralized SC's.