You can continue using IF for as long as you want. In fact, it's worth doing some form of IF indefinitely, if only for the health benefits. As far as weight loss is concerned, if you hit a plateau (which you will with any weight loss program), there are four things you could do to address this. These are:
1. Increase your fasting days/time periods (if you have only been doing relatively short or infrequent fasts).
2. Decrease your fasting days/time periods, and increase your calorie intake, for a couple of weeks to give your metabolism a boost. Then resume more frequent/longer fasts.
3. Reduce your calorie intake further during your eating windows.
4. Increase the amount of exercise you are doing to burn off more calories (but be careful with this as recovery will be impaired when on a calorie deficit).
You can't stick to exactly the same regimen and continue to lose weight effectively over the longer term. You will need to make some small adjustments over time, until you reach your final goal. Then find out exactly what you need to do to maintain it.