Thank you sammo.
Well, I already try that, but while soldering wires on those 3 pads for serial connection I ended up with just 2 of them. I overheated one (TX) and it is just not there anymore.
So, no serial connection for me on that device.
The only hope is that I can write firmware directly to the chip. I ended up with my RE450_bricked.bin and if I binwalk that binary, it is obviusly 2 U-boot loaders on wrong positions.
$ binwalk RE450_bricked.bin
DECIMAL HEXADECIMAL DESCRIPTION
--------------------------------------------------------------------------------
14608 0x3910 U-Boot version string, "U-Boot 1.1.4 (Dec 15 2017 - 15:14:42)"
14656 0x3940 CRC32 polynomial table, big endian
15952 0x3E50 uImage header, header size: 64 bytes, header CRC: 0x8555A513, created: 2017-12-15 07:14:42, image size: 39666 bytes, Data Address: 0x80010000, Entry Point: 0x80010000, data CRC: 0xD26A2F81, OS: Linux, CPU: MIPS, image type: Firmware Image, compression type: lzma, image name: "u-boot image"
16016 0x3E90 LZMA compressed data, properties: 0x5D, dictionary size: 33554432 bytes, uncompressed size: 106000 bytes
153892 0x25924 U-Boot version string, "U-Boot 1.1.4 (Dec 15 2017 - 15:14:42)"
153940 0x25954 CRC32 polynomial table, big endian
155236 0x25E64 uImage header, header size: 64 bytes, header CRC: 0x8555A513, created: 2017-12-15 07:14:42, image size: 39666 bytes, Data Address: 0x80010000, Entry Point: 0x80010000, data CRC: 0xD26A2F81, OS: Linux, CPU: MIPS, image type: Firmware Image, compression type: lzma, image name: "u-boot image"
155300 0x25EA4 LZMA compressed data, properties: 0x5D, dictionary size: 33554432 bytes, uncompressed size: 106000 bytes
194967 0x2F997 TP-Link firmware header, firmware version: 0.0.0, image version: "", product ID: 0x0, product version: 0, kernel load address: 0x0, kernel entry point: 0x80002000, kernel offset: 0, kernel length: 512, rootfs offset: 770417, rootfs length: 0, bootloader offset: 0, bootloader length: 0
195479 0x2FB97 LZMA compressed data, properties: 0x5D, dictionary size: 33554432 bytes, uncompressed size: 2207564 bytes
965897 0xEBD09 Squashfs filesystem, little endian, version 4.0, compression:lzma, size: 3634385 bytes, 669 inodes, blocksize: 1048576 bytes, created: 2017-12-15 07:25:27
4653056 0x470000 JFFS2 filesystem, big endian
Is it possible to merge somehow this bricked binary from chip with OpenWRT (or original) firmware and than write that newly prepared binary back to chip again?