Legend, that is NOT correct, you do not get back ALL of your tax paid for that year.
Your tax for the year is based on your taxable income less your allowances and credits. If you are made redundant in February and don't work for the rest of the year, the odds are that you will be due all the PAYE you paid back. However, the later into the year you work (or if you get a job after your redundancy) the more likely it is that you will only be due a small tax refund.
However, there are a couple of things to bear in mind.
Firstly, any statutory redundancy payment is entirely ignored for tax purposes. You don't pay income tax or PAYE on it.
If you receive an ex-gratia lump sum, a good chunk of this will be ignored for tax purposes (the amount depends on how long you've worked there, salary etc). To the extent that the lump sum is subject to tax, you pay PAYE and Health Levy only (no normal PRSI).
If you have a taxable lump sum, you will probably be entitled to "Top Slicing Relief". This means that if the rate of tax you pay on the taxable bit (which for most people would be 41%) is more than your average rate of tax for the last three years (which, taking account of the 20% rate, would be true of most people) you will be refunded the amount of tax paid on the taxable lump sum over that average rate.
Your best bet is to submit your P45 and last three P60s to the Revenue at the end of the tax year.