To cross Tibone you need to form column, or it can be crossed in any formation?
To cross you must lose half a move as usual, I presume.
Of course, it can't be crossed by a unit stepping backwards
This will be the testing point for the French...
The French player must take a critical decision which units to sacrifice.
Will he let the small pickets to defend the cascines?
Will he put any unit in Rottofredo?
Will he save the cavalry or at least part of it?
One last question: Can the French Dragoons dismount?
The French dragoons can dismount as always.
To just walk backwards is'nt as easy as it sounds, as the Austrians have some dashing commanders who easily could catch up the retreating units.
Our last Pfaffenhofen-Game is a good example. I had a lot of good luck to repell the fast Austrian flanking forces and sacrificed the Palatine troops, which were not overwhelmed too soon.
It would be typical to save the cavalry and artillery, as these troops were very precious and a lot more difficult to replace if lost (to exercise a horse until it is ready to serve as a warhorse is a real challenge). Sometimes nevertheless at least portions of cavalry were used for rearguard actions. Dragoons maybe would be a good choice, although using the HoW-rules will give you the Trouble to decide if the Brigade commander will acompany the retreating forces or the defending units.
You can form columns or cross the Tibone in line. To form columns would be difficult, as in my French list, the French need a full turn to change formation. Maybe to Change formation and turn would be an idea for the French second line, when the first line is condemned to repell the Austrian assault.
I would allow to cross stepping backwards. But it will be difficult enough. Walking backwards halve the move and crossing halve again. That would result in the French infantry cross with 3.75 cm in a turn (for my 1/72 scale).
To step backwards would most possibly create exactly the historical battle. Maillebois formed his army in battleline for several times to repell the Austrian pursuit.
By the way: I now included the French artillery on the map.