Alexban,
Re:
“Inflight, with a very low OAT, you can see all pumps illuminated, it happened this year to a few NG.”
This was a known problem on NG’s due to water trapped in the reservoir pressurisation system which froze when cold soaked and blocked the reservoir bleed air supply causing cavitation at the pumps. There is a mod available (SB 737-29-1106) which fixes this and another problem. You can tell if your aircraft has been modified because there is only one reservoir pressure gauge in the wheel well.
Re a double (or triple if you count the standby system) hydraulic failure on take-off: It has not happened in 38 years of 737 operations and I can’t see it happening, but nothing is impossible in aviation.
S&L