It looks like instawallet was a custodial service indeed so there is no way to recover the funds without the assistance of @Boussac. btw, it appears that Boussac is also the founder of paymium exchange which is still operational.
OP didn't login since a long time but luckily enough his email address is visible on his profile page. No guarantee that this is his main wallet or he is still using it but it won't hurt to send it a message and ask for an update.