Will whoever gets hold of this file be able to spend all zcash in my wallet?
Maybe a silly question, but I’m a new user, and thought there would be no harm in asking 
Yes, wallet.dat file has all the keys, if someone gets a copy they can use your keys to transfer money out.
If you suspect your wallet.dat is compromised, but the balance has not yet been transferred, quickly spend it to a newly created address either locally or at an exchange you trust to temporarily hold it.
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Thanks for the clarifications, Shawn and Kahooli!
The amount in the wallet is small- just a little test to get going. The thief is, most likely, waiting for a worthwhile bounty-
That said, I really like this whole project, and since I see an option (still greyed out, but…) for encryption, I assume this particular vulnerability will be taken care of in the not-too-remote future 
In the meanwhile I expect noone would use this wallet to store significant values, since Windows “security” is so clearly illusory.
On 'nix, this may not be so?
Cheers, and thanks again for your help!