How far to take legal proceedings when tenant has done a runner

Possession - Section 8 and Section 21

Hi,
I have a tenant that has done a runner, taken 95% of her belongings and left the back door key in the property, however still has the front door key.

She was 2 months into rent arrears and wouldn’t answer any of my phonecalls, so I have served a Section 8 Notice (through a solicitor), which is due to expire on the 31st March.

Given that the tenant has already left the property and not contested the notice as yet (and I believe she doesn’t have her post being re- directed so won’t have seen the S8 Notice), do I still need to complete forms N5 and N119 and go through the Courts for possession of the house?

Or can I get the house cleaned, locks changed and re- let without fear of being sued for unlawful eviction?

Thanks