The Charter of Fundamental Rights only applies to EU member states when they act within the scope of EU law. Therefore, it will no longer be relevant to the UK after withdrawal so the UK will not convert the EU Charter of Fundamental Rights into UK law. The substantive rights of individuals will not be affected because the Charter never created any new rights. The Charter simply brought together the rights that already existed in EU law into a single document to make them more visible.
The UK will remain a signatory to the European Convention on Human Rights because this is entirely separate from the EU.