1. Profits taken on investments held within an ISA during your lifetime are not subject to CGT.
2. Profits taken on investments held OUTSIDE an ISA during your lifetime ARE subject to CGT on disposal, on that part of the profit that takes you over the exempt threshold for the year.
3. Where investments are held until death, no CGT applies, as it is a tax on disposals during one's lifetime.
4. On death, the holdings within the ISA are transferred out into a normal non-ISA dealing account. The value they have on the date of death is the probate value (there is a complex little calculation for shares and similar, but it's not particularly significant).
I'll repeat : CGT is not levied on death, only on profits taken on disposals within your lifetime.
Therefore the WORST thing to do is sell everything that is not protected within an ISA on the DAY BEFORE you die, incurring massive capital gains tax (because you are alive), when deferring the intended cash-in by one day would have saved you all the CGT (because you were now dead and therefore CGT is no longer applicable).
5. And if the investments continue to grow in value after your death, before they are distributed to your heirs? It won't affect YOUR CGT, since you are dead, and not liable. It won't affect anybody else's CGT either, unless the increase is large AND the executors (or the subsequent owners) cash in too much profit in any one tax year. (Profit being sale value minus probate value). You may need to read HMRC leaflets (with ice-pack on head!) or consult a specialist on probate and CGT to get the full details.
Hope that's at least moderately clear, but do ask again if it's not!