As a Canadian NR, I don't believe you would have any problems with losing access to the funds and most services. The bigger issue IMO is that CRA uses having banking/investment accounts as one of the secondary indicators that one *is* a tax resident.
http://www.cra-arc.gc.ca/tx/nnrsdnts/cmmn/rsdncy-eng.html
I can see where one likely can leave the TFSA and RRSP as-is (in your case, you'd want to drain the TFSA before going to the UK) but beyond that, it gets murky as to how taxable accounts would be viewed or how much weight it have in deciding if you really were a NR.
If it does make sense for you to give up Canadian tax residency while leaving the RRSP intact - one will not be earning any RRSP contribution room until one is a Canadian resident again. The annual TFSA contribution room also goes away and where one left the TFSA intact, as a NR one can withdraw but can't put any money back into the TFSA.
If there's anything in a taxable account for investments, those will be deemed to have been sold at FMV on the date of departure.
http://www.mondaq.com/canada/x/217034/Income+Tax/Goodbye+Canada+HelloTax+Implications
Though if you plan on coming back anyway, I believe I've read where the owing taxes can be deferred and then when back in Canada - the departure reversed (unless one sells the investment first).
As for the "pull RRSP funds at a nominal tax rate of 25%. Would it be taxed in UK, thus negating the benefit?" question ...
This link seems to say where one's UK income is under $25K, the Canadian 25% withholding tax is the end of it. Over that amount, means it won't be worthwhile.
http://www.centa.com/article.php/20060727153645968
The HM Revenue & Customs bulletin at the links listed below seems to be saying the tax treaty sections to avoid double taxation are useless for the RRSP. The issue is that Canada taxes the RRSP withdrawal where there is no UK tax generated by a withdrawal. UK tax is generated when the assets are sold, which Canada does not tax.
It seems tax charges by both are required for the same event before there can be tax relief.
http://www.hmrc.gov.uk/manuals/dtmanual/dt4617.htm
I'd want to check with a qualified expert before making a decision.
Even when it seems simple (ex. the US), the more I read the more I'd prefer an expert. In the case of the US, I've heard for years that the RRSP is US tax exempt but then a more recent article advised a guy moving to the US to sell the investments in his RRSP then re-buy them. It seems that only the cost of the RRSP held investment is US tax free. The individual in question has a cost of $120K for what was worth $250K so that the sell/re-buy would bump the cost up to $250K (keeping it US tax free).
Cheers