This issue arises fairly routinely. Both because the facts are incomplete and this is a third-party report of what happened. Much easier if the "friend" posts directly.

First, this is not a matter for compensation, but rather a refund, under the terms of EC 261/2004. If the Regulation does apply to these facts, OP will be due a refund of 75% of the base fare paid for the segment in question. If it does not apply, he is due a refund of the fare difference.

Second, these situations do present a hard choice for the passenger. Carriers typically propose the quickest reroute which is what most passengers prefer. One might, however, tell the staff handling the rebooking that time is not of the essence and that accordingly rebooking on the next routing with PE available is preferred.