You're assuming that the D-Mark would be as strong (or possibly even stronger) as it was back then today. Which is a bold assumption. As a matter of fact, nobody (apart from some utterly ridiculous right-wing politicians) even considerers this an option.

If you literally mean that Germany was richer in the time before the introduction of the Euro, then simple GDP statistics show otherwise - not surprisingly, as it was a long time ago. If you mean the Euro was bad for the German economy, I wonder why you think that? By removing exchange rate risk, the Euro has made it easier for German businesses to sell to other Eurozone countries.