Hi VH
Shin splints...same here. Took a week off then resumed training, and it came back again. Frustrating so close to the goal.
So my advice is
(1) Don't rush back...you'll be tapering in a week's time anyway, so you're not missing as much as you think
(2) Buy a Mueller Shin Compression sleeve - very good compression / wear your Skins all day...compression is vital when there is so little blood flowing through the shins.
(3) If the shin splints are now chronic then rotate ice and heat 2min/off max 20 mins
(4) If you hate swimming try running in the pool. Failing that keep the aerobic conditioning up by getting on a bike/ rower / cross trainer. I did over 30 miles on the rower last week (couldn't manage a 1 for 1 mileage swap, but not far off...check what the bike conversion factor is...)
(5) Look on Youtube for shin stretches..daily dose to ease the fascia.
good luck...you've hit 20m so you should be fine