How long does it take to rebuild mileage?

Was supposed to (and still might able to!) run my first marathon at the end of July but got a mild hamstring strain (by essentially stretching the wrong way and not running somehow lol). I was already base building and running 35-40 miles a week (previous weeks before my half at 45 miles) with a max long run of 15 miles at the end of January and multiple 13 mile runs up until my injury. Saw PT and they want me to cut to 15 miles a week, max long run of 5 miles right now while strengthening and rebuild from there. They say I don't necessarily have to cancel my marathon but we'll wait and see. I was so proud of my long run skills and weekly mileage. I was going to be so prepared and ready- strength training, base building, distance- and now this. Anyone been through this and recovered in time for a race? I need hope!