I actually opened my account long before I actually moved here back when it was quite easy to do so. Post-2008 things have become very difficult as I discovered when a relative of mine asked me to do a few enquiries for him and I got PFO's from everyone other than PostFinance - although UBS was still open to it as long as he put a minimum of about 50k in.
My own bank has told me that I would not have any problems keeping the account open if I did leave, although I genuinely don't trust them. From what I gather, if your balance is under a certain amount (anything between 20k - 50k) you're just too much hassle for too little money, so if under that they'll either charge you silly fees to persuade
you to move on or simply inform you that you have to close your account.
Where you're moving to is important. A major EU country such as Germany, Italy or the UK will go against you. Moving to the US or even being a US citizen is likely a death sentence for your account from what I can see. However moving to many less aggressive
countries, even within the EU (such as Ireland, Portugal or Denmark) will likely suffer fewer restrictions - at least for now. Anywhere else (developing World, EFTA, etc) will be treated as business as usual.
So if you have multiple residencies (or an address) in a less contentious nation, citing that residency/address may be one approach - although I believe something like this was what Julian Assange had with PostFinance, which resulted in their closing his account as he allegedly "provided false information regarding his place of residence"
Another, although probably neither legal, practical in the long term or advisable
, is to not tell them anything and simply go down to your post office and have them forward your mail to your new address abroad.
As a final note on PostFinance; it is easier to keep a non-resident account simply because as it is not a bank, it is not bound by Swiss banking secrecy laws
. Probably not an issue for most, but if it is you should be aware of this.
My feeling is that, especially with most of the Kantonalbank's (i.e. not ZKB), you should
have no problem keeping an account open if your balance remains a minimum of between 20k to 50k (depending upon the bank and your future residency). If under, go for a PostFinance account as banking secrecy is unlikely to be that important to you. Of course, things are constantly changing in this area, so in six months or a year even these may not be options. Naturally the usual caveats on personal opinion, seek the advice of a professional first, et al. apply to the above.