Ah yes, now it's clearer 😉
If the euro disappears for political reasons, it will be replaced by a national currency, so assets will obviously not be lost. On the other hand, it is possible that it will lose value before being replaced by the new currency. More generally, even if the euro does or doesn't disappear, it's a good idea to vary your investments, in terms of currencies, allocation types and the securities making up each allocation. As you said, you can't put all your eggs in one basket.
To protect yourself against the euro, if it's your domestic currency, simply buy foreign currencies or securities quoted in foreign currencies. If you're just buying currencies, I'd advise you to aim for strong currencies such as the Swiss franc (CHF) or the yen (JPY). It would be foolish to invest in a currency just to protect yourself against the euro and lose even more money. The dollar is currently holding up well because of the Fed's policy tightening, but historically speaking it's a weak currency.
The choice of currencies is less important if you're buying foreign equities, as these tend to react inversely to their domestic currency, especially if they are exporting or commodity-oriented companies. In a pinch, you could even stay focused on European companies, which could benefit from a fall in the euro, boosting their exports.
One last option when the going gets tough: gold. The yellow metal loves it when currencies panic 🙂