Hi there.
Any advice to fly from Morondava to Toliara needs to be combined with a couple of warnings. First, there is – and according to Air Mad’s schedules will be at the time you want to travel – only one direct flight per week, and the route is served by a Twin Otter, an aircraft with only 19 seats. This means that you will need to plan and book a long way in advance, as the aircraft will quickly be full.
To give you some idea: I’ve just tried to book seats on a Twin Otter flight a long way into 2013, only to be told that the aircraft is already full – and that is on a route with three other direct flights a week with larger aircraft!
A further problem with Twin Otter flights is that they may not board your luggage due to weight restrictions. This happened to myself and my friends earlier this year. Not a great problem for us – our luggage was re-routed via Tana and we got it five days later, but if you’re not planning to spend five days in Toliara, it would be very inconvenient for you.
Apart from the one direct flight, there are other flights from Morondava to Toliara via Tana, but they are at least twice as expensive, and often involve a long wait in Tana. If you don’t get on the direct flight, it would probably make more sense to return by road from Morondava to Antsirabe, especially as the road is now very good. You could then do your RN7 trip north to south.
Twin Otter flights are in fact a fascinating experience – you fly low, and you see a lot – it’s just not as easy to get on them as #1 seems to suggest.
Do take great care if you want to look at sapphire digs around Ilakaka. There are many very unpleasant characters involved in unsavoury dealings there, and for many ordinary Malagasy the place has become a byword for gratuitous violence. I would advise you to use your time in Antsirabe to try and find someone who really knows the situation in the place and is prepared to accompany you there.
For tombs and spiny forest you should consider going down to Fort Dauphin and Adohahela National Park, although the time it takes to do that on unpaved roads may exceed your time limits.
Andringitra National Park is also excellent for camping and hiking, and you might like to compare it with Isalo and decide which of the two appeals most.
Other points on the RN7 which are well worth a visit are Anja Community Reserve near Ambalavao, and Zombitse-Vohibasia National Park.
The main reason people go down to Manakara as #1 suggests is the train trip from Fianarantsoa. At present, reports say that this has been suspended, so you would need to get information before incorporating that in your plans.
If during your stay in Antsirabe you are offered the services of a guide called Desiré who runs or ran a company called Discover Mada from the Hotel Baobab (he’s highly recommended in the LP guide) you will find that researching the recommendations of fellow posters on this forum and elsewhere in the internet will more than repay the extra effort involved.