There would probably only be 10 sections affected significantly. You can see all 5 on one side in this image:
https://seatgeek.com/venues/verizon-center/seating-chart/washington-capitals-3764/section-100/
Seats lost on the corners would be minimal (see the overhead chart with the maintenance tunnels leaving only a few seats rinkside).
If you count the seats it's about 12 in the front for the wedge shaped sections like 113, and 20 or so in the middle 3. So one row per side is around 85 seats for sake of argument, and about 170 per side so 340 which is under that 400 number I threw out but over 200. Even at 340 seats that's still a redistribution among 18,000 other tickets, which isn't that much.
But someone (chibi?) mentioned earlier, how much of this is practical with the renovation aspect? This view shows the problem clearly:
https://seatgeek.com/venues/verizon-center/seating-chart/washington-capitals-3764/section-103/
The concrete base at rink level of the VIPs might be OK to adapt to the new rink size, but the new VIP seats would be much higher than the current ones. It would be impractical to tier down one row as you'd need to change them all, and that would mean significant restructuring.
So imo it ain't happening, but not because of ticket loss so much as structural issues. The league is not going to gamble on a slight percentage increase in scoring at the cost of dozens of expensive arena makeovers.