Yes get well soon KP and MikeF. Bummer to be laid up for a chunk of the summer. But hopefully you'll be back at it in another month or six weeks.
I did something weird on Tuesday, just doing an early easy run because I didn't have time to do a full workout before an early work call. Stepped on a rock that all but went through my shoe (well not really but you get the point). So now I have a sore metatarsal--not terrible but it's there alright. Maybe a bone bruise, or just the soft tissue. So I took off yesterday and tried to rollerski a bit (first time in 6 years, and was definitely not really ready for that; it's actually more difficult than actually skiing and my coordination and balance have gone down some in those years). But still might add some in here or there as cross training.
About running in the heat, just use some common sense! In college we did workouts or races in the heat of the day sometimes (90s with high humidity), but that was because we had to. Post-college on those hot days I would do harder workouts late, after sunset, or early and would adjust pacing and duration. Learned how to adjust pacing for hot races, and actually beat better runners because I did adjust.
Per Tuesday, I could have done an hour plus with fartlek at 10 or 11 AM but it was already >90 degrees (dry here). So for my second workout did just 40 minutes with 8X 200 at moderate effort (5K/3K, working down to mile pace at the end). And it was on the turf to keep it easy on my foot.
I generally avoid hard workouts in the heat, and when I haven't however, have had some issues with thermoregulation after tempos run in the 80s or so. Overheated, then sweat like crazy, then chills, followed by overheating again and it takes a couple hours to balance.
One more time trial [5K] (tomorrow, at 6:30 AM to beat the 99 degree heat expected later in the day), and might take the weekend off to give that foot some time to heal up. Then I'm just going back to base work for the rest of the summer.