If i leave ireland then they cannot get the money sure?
How long before i would be allowed to come back with debt having been forgotten?
They can sell the debt to a debt collection agency abroad who will take e.g. a 10% cut of your debt owed to chase you down and get the money. These debt collection agencies are pretty determined and know every legal trick in the book (and some illegal ones, such as harassment) so they're not easy to escape. If you did want to escape them, the USA or China would be your best bet because as far as I know there isn't much legal reach into those countries from abroad. You'd struggle to get a visa for any country that requires one though as most require you to be in good financial standing in your home country so if you have an outstanding court order against you for non-payment of debts, you could forget getting a visa for e.g. the US.
If you go to the EU, on the other hand, it's easier for a debt collection agency to find you because the laws across the EU are more harmonised. If you did want to default, you'd be wise to get the visa for somewhere relatively impenetrable e.g. Russia or China first and then default from abroad.
I'm not advocating that though: you made your bed, so you should lie in it. If you want to play the bankruptcy game like the big players do then you need to have all your assets offshore to begin with and any properties in your wife's or family's name so they can't trace you etc. There are lots of tricks that professional conmen use but if you want to go on to live the life of a normal, respectable person then they're not really open to you.
Re your other question on bankruptcy: Bankruptcy in Ireland is only discharged after 12 years (AFAIK) and for that entire time, the courts can sequester your earnings and, if applicable, put you in prison for non-payment of debt at any time. If you're a solicitor, civil servant or company director that's the end of your career too. You're probably confusing this with countries like the US, UK, TV-land etc where bankruptcy is relatively painless. In the UK, for example, bankruptcy lasts 1 year although creditors can chase you for bills for longer depending on what was agreed. There are stories of people who went into negative equity in the UK in the early 90s still being chased for the debt into the early 2000s.
The banks should have been more regulated in their lending but what's done is done. You took out a debt and now you have to take responsibility for your situation. Without a nation-wide debt moratorium or overhaul of the bankruptcy laws, it's hard to see what's going to improve in the near future. Tried to find a link for you with a guide to bankruptcy in Ireland but there were no real sites I could find easily - maybe call MABS and see what information they have?