Hi Judy,
All ESA awards are indefinite, although there will be a reassessment date on the records somewhere.
ESA has no bearing on PIP. Everyone (under the age of 65 years in April 2013) on
DLA will be 'invited' to claim PIP at some stage over the next few years but the selection process seems to be random.
Your friend can contact DWP and initiate a PIP claim if they wish - but they need to be very careful about this if they are currently in receipt of DLa.. Once the process has been started there is no going back. If the PIP claim is refused, the DLA will finish 1 month later, no matter how much of the claim there should have been left to run.
I suggest your friend looks at our PIP self-assessment and scores it very harshly (as DWP will!) to see whether a successful PIP award seems likely.
PIP help for claimants