Cannot restore the startup disk as a single partition

Download the Sierra Installer from the App Store and re-install Sierra. Do not erase any partitions. Re-installation leaves non-macOS files untouched, but it is a good practice to backup your important files for safety. This will rebuild the Recovery HD.

We can manually merge disk0s[3,4,5] into Macintosh HD, but a missing Local Recovery HD means there are limitations. You can get local Recovery HD back using either TM or re-installation of the current macOS version.

For your own safety, I recommend disconnecting the 1TB disk till we can fix the issues with disk0.

The order of the disk slices is critical in the following command, otherwise you will lose data. Run

diskutil mergePartitions jhfs+ "Macintosh HD" disk0s2 disk0s5

diskutil list

and post the output.

Was this disk partitioned/modified using other tools? This does not look like a Recovery HD. What is the current macOS version?

nicojbn wrote:

diskutil list

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *251.0 GB
disk0

1: EFI EFI 209.7 MB
disk0s1

2: Apple_HFS Macintosh HD 141.4 GB
disk0s2

3: Apple_HFS BC1 650.0 MB
disk0s3

4: Apple_HFS BOOTCAMP 100.2 GB
disk0s4

5: Windows Recovery 471.9 MB
disk0s5

Did you run the following command..

diskutil eraseVolume jhfs+ BC2 disk0s5

You can try a SMC Reset and check the disk.

To rebuild the Recovery HD, you will need to download the Sierra installer from the App Store.

Can you post the output of

sudo dd if=/dev/rdisk0s3 count=5 2>/dev/null | hexdump -C

Here is an example from my Mac.

diskutil list

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *1.0 TB disk0

1: EFI EFI 209.7 MB disk0s1

2: Apple_HFS Macintosh HD 743.7 GB disk0s2

3: Apple_Boot Recovery HD 650.0 MB disk0s3

4: Microsoft Reserved 134.2 MB disk0s4

5: Microsoft Basic Data BOOTCAMP 255.4 GB disk0s5

6: Windows Recovery 471.9 MB disk0s6

sudo dd if=/dev/rdisk0s3 count=5 2>/dev/null | hexdump -C

Password:

00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

*

00000400 48 2b 00 04 80 00 21 00 48 46 53 4a 00 00 00 06 |H+....!.HFSJ....|

00000410 ce 97 4a 11 d7 8b e7 05 00 00 00 00 ce 97 ac 81 |..J.............|

00000420 00 00 00 22 00 00 00 16 00 00 10 00 00 02 6b e4 |..."..........k.|

00000430 00 00 58 74 00 01 fc ef 00 01 00 00 00 01 00 00 |..Xt............|

00000440 00 00 02 fd 00 00 06 96 00 00 00 00 00 00 00 01 |................|

00000450 00 00 02 ef 00 00 02 f0 00 00 00 00 00 00 02 ef |................|

00000460 00 00 00 00 00 00 02 ef e3 ee 9e 83 2e f5 f6 11 |................|

00000470 00 00 00 00 00 00 50 00 00 00 50 00 00 00 00 05 |......P...P.....|

00000480 00 00 00 01 00 00 00 05 00 00 00 00 00 00 00 00 |................|

00000490 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

*

000004c0 00 00 00 00 00 4d 70 00 00 4d 70 00 00 00 04 d7 |.....Mp..Mp.....|

000004d0 00 00 08 07 00 00 04 d7 00 00 00 00 00 00 00 00 |................|

000004e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

*

00000510 00 00 00 00 00 4d 70 00 00 4d 70 00 00 00 04 d7 |.....Mp..Mp.....|

00000520 00 00 42 10 00 00 04 d7 00 00 00 00 00 00 00 00 |..B.............|

00000530 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

*

00000560 00 00 00 00 00 4d 60 00 00 4d 60 00 00 00 04 d6 |.....M`..M`.....|

00000570 00 00 0c de 00 00 04 d6 00 00 00 00 00 00 00 00 |................|

00000580 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

*

00000a00

Do you have a Time Machine backup of macOS? If you do not, then do you have the Sierra installer?