FIA sporting rules section 16:
16.1 "Incident" means any occurrence or series of occurrences involving one or more drivers, or any action by any driver, which is
reported to the stewards by the race director (or noted by the
stewards and subsequently investigated) which:
a) Necessitated the suspension of a race under Article 41.
b) Constituted a breach of these Sporting Regulations or the Code.
c) Caused a false start by one or more cars.
d) Caused a collision.
e) Forced a driver off the track.
f) Illegitimately prevented a legitimate overtaking manoeuvre by a
g) Illegitimately impeded another driver during overtaking.
Neither driver may cause a collision, force a driver off the track, or illegitimately prevent a legitimate overtaking manoeuvre, or illegitimately impede another driver during overtaking.
So, blue can't ram into red. Blue can't force red off the track.
I also believe red is allowed to follow the track that you have drawn, since that would not be illegitimately preventing a legitimate overtaking manoeuvre.
I believe blue would be in violation of g) if it forced red to slow down in order to avoid a collision.
Further from section 20.4:
Manoeuvres liable to hinder other drivers, such as deliberate crowding
of a car beyond the edge of the track or any other abnormal change of
direction, are not permitted.
This also supports the red car in your diagram.
The only exception would be if the red car was being lapped by the blue car, in which case, the red car must allow the blue car to pass un-impeded at the first opportunity.