Varicella pneumonia is a most serious complication, especially in the immunocompromised host. Depending on how long the acyclovir has been given, you might wish to replace any anticipated usage of oral acyclovir with IV acyclovir.
Unfortunately, there is no good way to predict how long the acute respiratory distress syndrome (ARDS) will take to resolve and resolution may slowed, if the Varicella pneumonia has not resolved. Treatment of the ARDS should be continued until there is clear evidence of resolution on x-ray.