If you allow the company to be struck off involuntarily then you run the risk of being disbarred from acting as a company director in the future and also potentially being brought to court for non-submission of returns.
That's the theory anyway.
In reality (AT THE MOMENT) I have NEVER seen a person barred from acting as a director for allowing a company to be struck off and I have NEVER heard of a director being brought to court for non-submission of returns.
That's not to say that it won't happen in one year, two years, ten years or more but it's not happening now anyway.
If you decide to just let the company die off without getting it struck off properly then they are the potential consequences so just to make you aware of that.
If you decide to do the right thing then there is no way of avoiding any of the penalties or late charges. You need to get this sorted ASAP or it will become very punitive. If you file an annual return tomorrow online then this will stop the clock in terms of penalties for 28 days.
The first problem is that you will have to have your accounts audited for both this year and next year. You need a registered auditor (not just an accountant) and they need to file the accounts up to date and then you can get the company voluntarily struck off.
If you find a nice auditor you may be able to get it all done for €1,000 (incl CRO fees) but I would be amazed if you could get it done for less than that TBH.