Well, an opiate is a opiate. Switching to methadone doesn't mean that you kicked your hydro/oxy/heroin addiction, it just means you're now using methadone instead, which is way more potent mg for mg. in essence, you really just raised you're tolerance a lot so quitting cold turkey now would be harder than before you got on methadone. Even seven days of 40mg of methadone is enough time to raise your tolerance considerably. Luckly though, it hasn't been so long that the methadone has really begun to stack up on itself, so you probably don't have much more than fourty mg in your system at any given time. If you continue to go to you're clinic every day, the dose will stack up and you'll probably accumulate a much higher total amount of methadone in you're system, probably twice as much as you're daily dose. So that will mean that detoxing from fourty mg will really be like detoxing from a total of 80mg (maybey a little less, I havnt looked at a methadone half life graph showing accumulation), so after 24 hours or so, you'll still have fourty mg, 48hours, 20 mg etc..
It wouldn't be the end of the world, a lot of people take 100mg+ a day, but if you want to quit before methadone really has its grip on you, now is the time.
Otherwise I would just use the methadone for maintenance for as long as you need to get your life back in order, and when the time is right taper off. Either way you got to make up you're mind relatively quickly as to what you want to do, because methadone is something that requires commitment, and it sounds like you're having doubts about the whole thing in general (which is perfectly appropriate as methadone maintenance is a pretty serious form of ORT)