back at it
If your were cross training at an equivalent effort level as running, you will still be in great aerobic shape after 5 weeks on the elliptical. However, your "running" legs will need a few weeks of lowly ramping up, so that you don't get reinjured or get a new injury. I'd mix the running with cross training, gradually decreasing the cross training as the weeks go on. After 5 or 6 weeks, you're back to your full running load.