In defence of the LA's etc, Capita provide break-fix support, LA's provide that, via Capita, along with "how do i?" support. Break-Fix is a must, you can't avoid it. LA's get a percentage back for doing the donkey work. They tend to bulk it up by embedding training and also offering cheaper training, so instead of pay £1k to Capita you can pay (I'm guessing) £400 to your LA.
The only problem I see with Sivadam school is what happens when he leaves. Hopefully they are large enough and wise enough to have staff to pick everything up when he does leave and they are not silly enough to think SIMS users - aka admin staff, are easily replaceable. Long go are the days of schools hiring high level math teachers.
Although SIMS is very simple to learn it doesn't get the most out of it, like Sivadam is doing day after day, nor will it be as smooth and trouble free!!
IMHO you need at least 3 SIMS experts to cover the bulk with a nice bit of cross over with regards to knowledge. If you don't have this, you'll need a training\support deal. They need to be local, they need to be able to visit and offer onsite day visits, so if you need a timetabling creating, or cover 7 doing for a few days along with other bits, they can offer such a thing or at the very least give you a helping hand.
Now whether this is "Capita", your LA, another school, a 3rd party or Joe's fish'n'chip down the road, I guess it depends on the cost, quality of service etc.
Out of interest, how much, if they can, does Capita charge if your LDF becomes corrupt because of your backup (or such) and you have no valid backup?