Hydropneumatic suspension - Wikipedia

Failure of the hydraulic system will cause a drop in ride height and, possibly, the failure of suspension completely, and the brakes will not work. However, an acute failure will not lead to acute brake failure as the accumulator sphere holds enough reserve pressure to ensure safe braking far beyond that needed to bring a vehicle with a failed system to a standstill.

...The 2003 Citroën C5 has continued development of Hydractive suspension with Hydractive 3. Compared to earlier cars, the C5 stays at normal ride height even when the engine is turned off for an extended period, through the use of electronics.

The C5 is the present successor of your BX. Citroën C5 - Wikipedia

In a major break with Citroën tradition, the brakes and steering were no longer powered by the same hydraulic system as the suspension. It has been speculated that the primary driver for this was the cost of developing electronic brake force distribution for the system when the PSA Group already had an implementation for conventional brakes. Another factor may be the highly responsive nature of Citroën C5 brakes, which some have found hard to adjust to on other hydropneumatic cars, though it is felt by some to be superior. It can be scary for a C5 driver used to the instant reactions of an older hydropneumatic car to drive another vehicle and find an inch of pedal travel before any significant braking is achieved.

Also, perhaps surprisingly, according to the German motoring club ADAC's benchmark accident statistics classification (2007, pdf!), the C5 doesn't feature due to low selling numbers in Germany, but Citroëns are rather good.

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