Get new bolts before starting the job. Use heat to remove the old ones if stuck.
So you're hearing they snap? Where from? You never know, your experience may be different, so worry about crossing that bridge when you get to it.
If the bolt head shears off, it'll be subrame(s) down to remove the remainder of the bolt. If you're lucky there will be a stub to grip onto. If snapped off flush.....have fun with the drills and taps.