It´s not that much of a problem - how often do monarchs change? Every 20-30 years on average? And it wouldn´t be like every coin is withdrawn and replaced - no, just the new coins will bear the new face.
By the way, did you know that the way the monarch looks changes every time there´s a new king/queen? left-right-left-right, and so on.
I don´t really think the UK will join the Euro. The politicians as well as intelligent citizens have realised it would be a great advantage, but as long as Sun, Mirror and the like control the voters´ brains... no way.
Anyway, the Euro coins´ back is indeed the "national" side - the monarchs you´ll find there are the respective kings and queens of the Netherlands, Spain, Luxembourg, Belgium, Monaco and the pope. (So IF the UK joined the Euro, there would be Mr. or Mrs. Windsor on them.)
The notes are all identical.
I´ll have a great time fishing out one coin each out of circulation!
Here´s a great website featuring ALL Euro motifs which are already known:
On the first page is the common front, click on the flags to see the backs.
>>The French have pretty cool monies. I brought about $20(USD) worth home for my son. He collects 'funny money'.
well, yes. But our German coins are so boring only because they haven´t been changed for over fifty years - where else do you find coins from 1948 in normal circulation? (Talk about stability here