7 weeks off running, what is the likely effect?

it will probably do you some good and invigorate your running when you get back.  you'll lose less fitness than you think as you will carry muscle memory.  if you can tick over while you're way then that will help but don't sweat it.  many if us have longer out with injury but if the base is good, it comes back readily.

We're all different, and it depends on age and various other factors, but in my experience it takes as long as the time out to regain *most* of the fitness lost and as much again to get back that final 10 per cent or so.

If I were out of it for 7 weeks I'd resume with the first week or so just gently easing myself in then take it from there. But you probably don't need me to tell you not to overcook it when you start over ...

In fact, taking a month or two off once in a while is no bad thing.

about 2 weeks....but depends on how much lack of exercise, boozing and eating you do in those 7 weeks!!  if you manage to stay exercised and stop putting the pounds on, then it won't be long

Whereas my answer assumes you do nothing during the 7 weeks ...

i'd suggest any cardio work you can do at all during the 7 week running hiatus will help slow down the fitness decline and put you in a better position when you return. i you can't run, perhaps swim, hike, cycle, even a brisk walk regularly. Your cardio fitness will likely be the quickest to decline, but the quickest to regain too. You're unlikely to suffer major reverses in your muscle development during this time.

the fewer pies and pints you can swallow, the better

When you get back, you'll probably be about the same level as I am now.... 

In terms of your ability to go out and run, you should see hardly any difference at all. You will lose a little speed and conditioning, but your base fitness level won't fall that much, and some of the loss will be offset by a decent rest and recovery.

If you were in the middle of a very structured programme, say building up to a marathon, then you would have to be more careful coming back in. Often quoted advice is to start back behind where you left off, and then take the same amount of time as you had off to get back on track with the programme. In your case I'd say come back and have a week of 3 or 4 steady runs of normal distances, and then gradually incorporate anyspeed sessions in the following weeks. 

A data point: every spring I get up to marathon form at about WAVA 67% level ie reasonably good club but not county level. Then I have four weeks summer holiday, three of which i hike typically 15 miles a day average. If I do no running on top of the hiking, or even only a bit, I find a lot of the form has gone and it's very frustrating getting back up to speed. It takes at least two weeks to get most of the way there and say a month until I feel happyish. It'

Having said that, I tend to set mara pbs in the second half of the year, after coming back in form for 6 weeks or more. So the "rest" and change of activity could be seen as a way of double-peaking for the year. Plus the fitness of your bones, joints and sinews takes a lot longer to decay than aerobic fitness and muscles.