The Vivaro is renowned for "eating gear linkages" and it litterally does, especially if you drive round town all the time.
As a temporary fix and I mean till you can get it to the garage the same day, you can clipe the linkage back on.
If you open the bonnet, the gearbox is located on the right hand side at the bottom of the engine. If you look into the compartment, you'll probably see a cable with a round end, normally a black cable with a white disc attached to the end, not attached to anything. near it you will find a little metal knob, which protrudes from the gearbox. This is difficult to spot if you don't know what you're looking for. The white disc has to clip onto that little knob.
Paul Krynauw
December 2010