Complex sentence: It is not known when William was released on this second occasion, but it is notable that he did not lose his estate and was able to pass it on to his son after his death in 1654.
Split into simpler sentences: It is not known when William was released on this second occasion. However, perhaps more importantly, Sir William was able to avoid the sequestration of his estate during his two periods of imprisonment and was able to pass this on intact after his death in 1654.