How carb depleting is a 1hr weight training session?

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So if someone is on a low carb diet then it would make sense to do weights first then cardio?

I think what I'm actually asking is, will glycogen get restocked fully i.e 300g in the muscle's and 100g in the liver, through other mechanisms (glycolysis) if dietary cho is low? I'm guessing not?

300g of muscle glycogen is quite a modest amount - if you are not training heavily on successive days I don't see why it would not be replenished to that sort of level. A lot will depend on total protein intake. I've read that 100g of protein is required to synthesise 57g of glucose via gluconeogenesis. If you train every other day at the same time then, theoretically, you are not training more frequently than every 48 hours, so potentially 114g of glucose could be synthesised in that time. If you are not training the same muscle groups from one session to the next, then obviously that can be potentially doubled or more. If you start of with full glycogen stores (say 300g) and you don't deplete much more than 25-50% of that per training session, it becomes doable - especially if you take into account that 300g of muscle glycogen is distributed among all of the skeletal muscles and you only use up the glycogen in the muscles actually being worked. Another mitigating factor is that, on a low carb diet, you should be optimally adapted to using fatty acids and ketones which, as the studies already quoted indicate, could spare glycogen usage by up to 40%.

So much depends on intensity, volume and frequency of training and how you split muscle groups throughout the week.

Just as a very rough example let's say you split your muscle groups up into three training three days a week every other day. So, on average you will be using up to 50% of a third of your total muscle glycogen stores each session (300g/3 x 0.5=50g) as one of the studies showed, around 25-50% of that could be replenished in the first 2 hours of passive recovery in the absence of caloric intake (~12.5-25g) leaving just 25-37.5g to replenish before those muscle groups are exercised again. Of course, you have liver glycogen on top of that, which may take precedence.