We've just had the first flights in this afternoon (albeit positioning flights) which are for outgoing flights to Canada. The theory is that rather than try and clear the backlog of passengers, the airlines will, after getting passengers back home, start again from "Year Zero" so to speak.
In other words, rather than trying to get people who should have gone on holiday last Saturday out to Spain, or wherever, they will just start with those who are due to fly out in the next few days. On that basis, as long as the volcano doesn't start up again, you should be alright.
But, just to be on the safe side, check your holiday insurance covers you for "Acts of God." If you're booking a complete Inclusive Tour package you should also be covered by ATOL and the like.
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