Data should be backed up whenever it is at risk.
There is no automatic data loss when converting from basic to dynamic.
GPT or MBR can be converted from basic to dynamic.
This link may be useful:
Frequently asked questions about the GUID Partitioning Table disk architecture
What happens when a basic disk is converted to dynamic
For a drive to be eligible for conversion to dynamic, all basic data partitions on the drive must be contiguous.
If other unrecognized partitions separate basic data partitions, the disk cannot be converted.
This is one of the reasons that the Microsoft Reserved Partition must be created before any basic data partitions.
The first step in conversion is to separate a portion of the Microsoft Reserved Partition to create the configuration database partition.
All non-bootable basic partitions are then combined into a single data container partition.
Boot partitions are retained as separate data container partitions.
This is analogous to conversion of primary partitions.
Please remember to vote and to mark the replies as answers if they help.
On the bottom of each post there is:
Propose as answer = answered the question
On the left side of each post there is /\ with a number: click = a helpful post