The wallet is very secure. I have around $4000 here and am not worried. A lot of people have a lot more. Market price is more of a concern.
Steem Power is locked in Steem which you can withdraw but you get around 1% out each week for 2 years so it takes awhile to get out...but does 2 awesome things. It protects you against most of the inflation (each minute or so that you hold Steem Power..it grows), and it also gives you part of your voting power.
Steem dollars can be withdrawn any time and earn 10% Apr. Steem doesn't help with voting power and doesn't grow to help against inflation.but it is liquid.
I don't see Steemit forking gor lots of reasons. Most people will stick with this website and a fork would have to use another website. If someone tried to make a Google clone at Groogle..no one would use it.